Learn more about what bend relief is, when it's required in metal bending & the benefits of using bend relief today!
Hole positioning is an essential aspect of custom sheet metal part design. Though engineers often rely on CAD or other design programs when placing holes in their designs, it's important to consider how the fabrication process will impact their performance. Placing a hole too close to a part's edge or bend radius can affect its durability, appearance and function.
When you send a part design to manufacture, you expect the final product to look and function how it does in your plans. As a result, you need to plan hole positioning correctly the first time. Understanding hole positioning in sheet metal fabrication can save you time and money and help your manufacturer deliver the results you're after.
What Happens When a Hole Is Positioned Improperly?
A hole placed too close to the edge of a sheet metal part has the potential to affect performance. Designed to attach the part to another component using a rivet or other fastener, the hole and surrounding metal may tear or crack, compromising the structural integrity of the product. This effect worsens as more force is applied. Depending on the application, this cracking can decrease the part's lifespan or even make it unusable.
When a hole is placed too close to a future bend in the metal, it can become warped during bending. This warping occurs when part of the hole is affected by the pull of the bending process. The bend drags the surrounding metal and changes its shape, resulting in a deformed hole that's difficult or impossible to accurately thread. The only ways to avoid warping are to drill the hole after bending, which can be expensive, or to move the hole position farther from the bend radius.
Calculating Minimum Edge Distance and Bend Distance
Selecting a hole position too close to a part's edge or bend radius can significantly impact the performance of the final product. Fortunately, calculating a better hole placement is usually simple.
For applications where hole placement must be near the edge, the hole distance from the edge should always be equal to or greater than material thickness. Keep in mind, however, that some applications require more distance. For example, you may want to increase the distance to 1.5 times the material thickness or more for complex designs in the material handling or construction industries.
To calculate how close a hole can be to a bend, you need to use a different formula. In most cases, minimum hole bend distance equals 1.5 times sheet thickness plus bend radius, though the multiplying factor may increase as hole size increases in diameter.
Though these calculations can help you approximate the minimum distance you'll need to place between a hole and the edge or bend in sheet metal, different situations call for different specifications. Other factors to consider include:
Contact the Fabrication Experts at APX York Sheet Metal
Proper hole positioning helps ensure a smooth fabrication process and a final product that performs as expected. At APX York Sheet Metal, we have 71 years of experience in custom metal fabrication. If you need a manufacturer capable of managing precise hole positions in sheet metal, we can help. Contact us for a free quote today to see how we can manufacture your design.
Learn more about the causes of sharp bends in custom part fabrication & how to avoid them. Call today for metal bending services!
Sheet metal bending is a vital and common manufacturing process used in many American industries. Sheet metal forming, as this metal-working task is also known, is invaluable for making diverse products like original equipment in large construction machinery to small but specialized components in material handling logistics systems. A great part of the nation’s economy would be severely curtailed without effective sheet metal bending techniques, equipment and expertise.
Sheet metal bending entails taking flat metal stock from sheets and applying force or pressure to change its shape into the desired configuration. Manufacturing presses can be powered pneumatically, hydraulically or electrically. Also, they range in capacity from light-duty punch and die sets to massive presses capable of applying tons of force to bend and permanently alter thick metal.
Regardless of size or power, all sheet metal bending techniques take standard variables into account when planning a job. Sheet metal forming technicians need to calculate metal springback reaction and compensate for metal bend allowance. Calculating sheet metal bend allowance and knowing how to reduce springback takes considerable expertise and requires professional knowledge to consistently produce top-quality end products
What Is Bend Allowance?
When technicians bend sheet metal from its original flat and straight shape to a bent configuration, they also change its physical dimensions. The metal’s length and width elongate because of molecular action and the laws of physics and mathematics. The force of bending the material causes material at the bend point to compress on the inside of the bend radius and stretch on the outside. This causes the metal stock’s external measurement to grow.
This physical deformation increases the material area in a finished product compared to the length of the original stock. This increase might be slight for simple end products requiring only one bend, but they can drastically alter the amount of sheet metal needed to produce a product with multiple bends. Product designers and professional fabricators compensate for the change in material dimensions by building in bend allowance into their starting measurements.
To understand what occurs to cause dimension changes in formed sheet metal objects, it’s necessary to know the physical and mathematical forces that occur when a metal sheet experiences tremendous pressure. Bending metal requires altering the molecular state of an inert object into a newly formed product. Those two states are:
Elastic: This is where the metal is bending or stretching. It’s much like how a rubber or elastic band reacts under force. The elastic state is only momentary while the metal goes through the forming press or brake. Elasticity causes metal surfaces on the outside of the bend to experience tension forces, while the inside of the bend’s radius goes through compression. Compression increases molecular density, while tension decreases density. Therefore, the metal on the outside surface expands its length while the inside surface shortens. The tension force must always be greater than compression or the metal would exceed its yield capacity and break.
Plastic: This is the inert or stable condition an object is in before and after it experiences forces putting it in an elastic state. Although a metal product may be in a physical plastic state, it can still be under tension and compression. However, a plastic object will have stable dimensions even if it grows or stretches during a bending operation. The difference in length between before and after the bending process is an important allowance that sheet metal fabricators need to calculate when preparing materials.
While calculating bend allowance, or bend deduction, is somewhat predictable, it isn’t an exact science — too many variables exist. Some of the factors influencing bend allowance include:
Material Composition: Metals with soft properties are more elastic than hard materials.
Material Thickness: Thicker materials will stretch more than thin products when bent.
Material Grain: Cross-grain bending reacts differently to straight-grain bends.
Temperature: Warmer materials are more elastic than cold metals.
Die and Punch Sizing: Bending tool design affects metal stretch.
Pressure: Force inside the press or brake also affects plasticity.
Designers, engineers and fabricators use mathematical calculations to determine sheet metal bend allowance. One of the core math elements is called the K-factor, which is a neutral axis line inside the sheet that runs horizontally with the metal between the inner compressed surface and the exterior under tension. While the inner surface within the bend area contracts and the outer dimension expands, the neutral — or K-factor — dimension remains constant regardless of material thickness and severity of the bend.
K-factors are the ratio of compression to tension forces occurring within the sheet metal bend. Their values normally range in the 0.25 area but can never exceed 0.5. This is because it’s physically impossible for compression at the bend’s inside to be greater than tension forces on the outside.
The K-factor axis is a control figure used to determine the bend allowance and forecast precise material requirements before altering the metal’s configuration. This can be a complex figure to calculate. Fabricators often refer to charts which table K-factors. This is a historic approach within the sheet metal fabrication industry, but today, advanced software programs are available for computer-assisted design.
Another significant factor contributing to bend allowance is the type of bending process a fabricator selects. Each one results in different plastic and elastic forces being exerted on the sheet metal material. These are the three common processes used in fabrication brakes:
Air Bending: This is the most popular brake style and the easiest to use. Air bending incorporates an open brake design where the outside radius of the bend does not contact the die face. Air bending doesn’t require as much force as the other two brake designs. However, the downside to air bending is a phenomenon called springback, where the elasticity remains in the metal after the brake releases and tries to spring back to its original shape. Springback is another important factor that fabricators need to calculate and allow for in the bending process.
Bottom Bending: In this brake design, the sheet metal makes full contact with the die. Bottom bending requires more force than air bending and is used for thicker and harder sheet metal materials that need full compressive power to move between the plastic and elastic states. A drawback to bottom bending is the time and energy required to complete bends. However, because bottom bending crushes the sheet metal, it removes most of the residual elasticity that causes springback.
Coining: The earliest sheet metal brakes and presses utilized the coining process, which is similar to stamping out coins. Coining is a bottom bending approach that forces the punch into the die seat. It requires considerable force and can weaken the material within the bend radius. Coining can prevent practically all springback, but the weakening effect is often a disadvantage.
Bend allowance is sometimes referred to as bend deduction. The two terms are similar but not exactly equal. Bend deduction is a reverse calculation where the additional stretch measurement is deducted or removed from the material requirement calculation. This might be a cart-horse issue, but all sheet metal fabricators know how important bend allowance is to their finished products.
The Importance of Bend Allowance
Calculating and compensating for bend allowance is highly important for accuracy in finished sheet metal products. Anticipating bend allowance is a core principle for designing and fabricating precise products that perform with perfection. Ignoring bend allowance measurement would result in a poor fit and finish as well as possible end-product failure.
Bend allowance might not seem important for simple sheet metal work like building flashing or manufacturing material handling devices like shelving. However, calculating bend allowance has a cumulative effect that increases the margin of error when developing complex products with multiple bends required from a single stock of sheet metal.
Metal housings for electronic components are a prime example of how important bend allowance is to the accuracy of finished products. Bend allowance is also highly important to precision-driven industries such as custom sheet metal fabrications for industrial enclosures and environmental solutions. Original equipment manufacturers (OEM) also expect exact bend allowances for their important sheet metal works.
Although bend allowance is an extremely important function of sheet metal craftsmanship, it’s not the only calculation and anticipation involved in designing and making metal products. Springback reactions also occur when forming sheet metal bends and anticipating springback values is also a critical design factor. Bend allowance and springback calculations go hand-in-hand with professional sheet metal production.
What Is Springback in Sheet Metal Bending?
Springback is a physical function of sheet metal bending. When sheet metal stock transforms from a plastic state, into an elastic condition and then back to a newly configured plastic existence, the metal’s molecular properties can retain its original instructions. This is similar to the metal having a memory and trying to reestablish its past.
In other words, the metal is trying to spring back into its initial state by retaining energy and transforming it into a reactive force. This is a natural phenomenon that occurs in metal, and knowledgeable fabricators always take springback forces into account when building precise sheet metal products. They are also aware of these contributing factors that determine how much springback to expect:
The material’s chemical composition
Yield strength in the material
Physical properties in the metal such as grain
Material thickness and overall size
Brake or press design being used
The temperature of the sheet metal and tools
Deformation rate known about the material
Bend radius prescribed by the product design
Bend allowance factors anticipated and factored in
K-factor ratios also play a big role in calculating springback in sheet metal fabrications — so do trial and error prototypes, as well as personal experience of the fabricator. Like bend allowance, precisely determining springback isn’t completely predictable. That’s especially so when working with newly designed sheet metal products and unfamiliar materials.
Fortunately, professional sheet metal fabrication companies have experienced staff using state-of-the-art equipment to compensate for metal springback.
How to Compensate for Metal Springback
Nothing beats personal experience when it comes to knowing how to compensate for metal springback when working with sheet metal. Knowing the factors affecting springback is highly important — so is having the right type of equipment, applying either an air bending, bottom bending or coining process.
Experienced fabricators start production by building their material’s known properties into their springback calculations. They also compensate for springback by using the precise pressure required for the bend and the radius degree they’re planning to achieve. Then, professional metal fabricators use a technique called overbend.
Overbend occurs exactly how it sounds. Fabricators account for a calculated springback occurring in their material and literally bend the material over the finished radius point, so the metal will spring back into the precise angle expected in the finished product. Top-end metal fabricators use natural springback forces to their advantage, not their disadvantage.
While springback happens from strain and stress at the molecular level, custom metal fabricators see them playing out on the surface in their everyday sheet metal projects. Precision fabricators overbend their seams exactly enough so the elastic recovery stops at their desired point. Inexperienced fabricators can go too far with overbends, though. Excessive bends can result in a ruined product, while insufficient bends require inefficient re-bending. Neither of these mistakes will happen when professional sheet metal companies undertake custom metal fabrication.
Considering Bend Allowance & Springback During Custom Metal Fabrication
Experienced custom metal fabricators always consider bend allowance and springback when designing and manufacturing end-use products. It’s part of the professionalism expected from these highly-skilled craftspeople. They’re used to extreme tolerances when creating custom pieces for exacting customers.
While experience is a key component in manufacturing custom sheet metal work, these fabricators would suffer without precision bending equipment and excellent material to work with. They also need to be familiar with other sheet metal manufacturing services such as laser cutting, welding, grinding and powder coating. This is where a professional custom sheet metal fabrication company like APX York Sheet Metal excels.
Contact APX York Sheet Metal for Custom Part Design & Metal Bending
APX York Sheet Metal has more than 70 years of experience in custom part design and metal bending. Since 1946, our business steadily evolved into the leading sheet metal fabrication shop in Central Pennsylvania. We efficiently manufacture tailor-made products instead of relying on products made of stock sheet metal.
Our 65,000-square-foot facility is a single provider for all custom sheet metal work, including design, fabrication and finishing. By streamlining operations, we have increased efficiency to bring your products from a concept to a conclusion in short order. Our custom sheet metal fabrication facility serves all of Central Pennsylvania and Northern Maryland. We focus on delivering top-quality products at competitive prices with excellent customer service.
With state-of-the-art equipment and advanced business processes, our skilled staff rise to meet your sheet metal challenges no matter what they might be. Our in-house expertise, equipment and technology provide you with fast turnaround time on small and large orders. Call APX York Sheet Metal at 717-767-2704 to find out more about our product design and metal bending services. You can also reach us any time through our online contact form.
When you hear the term corrosion, you likely think of old, rusted metal. You might think of the orangey-brown tones of an old wagon wheel or the reddish hues of a deteriorating ship hull needing paint. Or, you might see automobile graveyards where once-classic cars rust back to their original iron state.
Corrosion is a natural occurrence that happens with all metal products over time. What you might consider "rusting" is just one form of corrosion where iron and steel products oxidize in the presence of oxygen and water. Many other metals suffer corrosion threats including aluminum, brass, bronze and even the highest stainless steel grades. Fortunately, metal corrosion is preventable. Corrosion protection can save the American economy vast sums lost annually by nature’s energy cycle built into metal.
The National Association of Corrosion Engineers (NACE) is considered a worldwide authority on corrosion, with members worldwide who collaborate on solutions to control corrosion. According to their 2016 International IMPACT Study, corrosion damage has a global cost of $2.5 trillion annually — a significant amount that could be saved with proper corrosion protection practices.
Despite corrosion being such a massive cost to the global economy, the fight to control and prevent corrosion gets little attention. Corrosion affects almost every part of daily infrastructure from transportation to utility providers. It can also result in catastrophic events like airplane crashes and bridge failures that cost money and human lives. Preventing metal corrosion and its far-reaching effects start with understanding what causes corrosion.
What Causes Corrosion?
To understand the causes of corrosion, it’s necessary to know what corrosion is. The National Academies Material Advisory Board (NMAB) defines corrosion through two National Research Council reports. Corrosion is the deterioration or degrading of a material’s physical properties through chemical reactions within its environment. Although non-metallic substances like glass, plastic and ceramics can technically corrode, by far the most common corrosion processes occur with manufactured metals.
The term corrosion comes from the Latin word corrodere, meaning “to gnaw to pieces,” which has the similar root word “rodent.” Corrosion is the slow destruction or eating away of things, which has a literal application such as with rusting or abstract implications like corroding emotions or relationships. In the material world, the highest risk for corrosion is metal.
Oxidation is the most prevalent metal corrosion form. Oxidation corrosion happens when metal objects react with oxygen and a fluid environment like air or water to form a more stable thermodynamic state. Synthetic metals are the highest risk for corrosive oxidation because they were changed from their original ore state by adding energy to create new compounds and alloys.
These manufactured products exist in a higher energy state than their ores once were. As part of a natural cycle, these materials release energy through corrosion in a long-term path of returning to their original state. When metal atoms such as iron experience oxidation, they release negatively charged ions that build up in the material and exacerbate the corrosive process. At the most basic form, corrosion is an electrochemical process. However, there are different causes.
Primary Causes of Metal Corrosion
In general, five main causes of metal corrosion can occur, along with some other less common reasons. Each contributing factor can act alone or in unison with another. All occur wherever metal has an active environment that’s suitable for creating corrosion.
1. Atmospheric Corrosion
By far, the most common form is atmospheric corrosion. It’s also called uniform or general corrosion. This is where oxidation takes place across a metal object’s entire surface that’s exposed to atmospheric conditions. These conditions include air or oxygen, moisture such as rain, snow, ice or dew, sunlight, airborne pollutants and temperature fluctuations. Although atmospheric corrosion typically happens in an open environment, the same processes occur underground and underwater.
2. Galvanic Corrosion
This corrosion cause occurs when two dissimilar metals electrically engage when they’re mated in a manufactured assembly. Galvanic corrosion, or bimetallic corrosion, happens when one material creates an electric charge that’s passed to the other causing an electrochemical event. The terms “noble” and “active” are associated with galvanic corrosion. Noble metals (cathode) are more inert than active (anode) metals. The further separated cathode and anode electrochemical reactions are, the faster they break down the affected metal.
3. Crevice Corrosion
This is a common corrosive cause in products manufactured with metal. Every assembled product has crevices like joints or seams susceptible to invasive conditions that bring on corrosion. Those crevices can also be cracks, splits or gaps occurring through wear and tear during a metal object’s life cycle. Crevices in shielded areas are at the highest risk for corrosion. These micro-environments create perfect conditions for trapped moisture, stagnant solutions and depleted oxygen. Often, crevices get contaminated with chloride or salt, which significantly speeds up corrosive electrochemical reactions.
4. Pitting Corrosion
Pitting usually occurs on a metal object’s exterior where it is uniformly exposed to atmospheric conditions, but the surface has been protected by a film like plating, painting or powder coating. Over time, tiny holes perforate or pit the protective coating and allow subsurface penetration of water, chemicals and oxygen. This also creates a mini-environment under the film which is virtually invisible to the naked eye. These pits grow under the film surface until they blister and present themselves. By then, the corrosion has caused significant structural damage.
5. Microbial Corrosion
This form of corrosion happens when unprotected metal stays in contact with sludge or soil. Both air-bearing (aerobic) and air-void (anaerobic) conditions lead to corrosive action. Excessive water presence accelerates microbial growth, which literally “eats away” at the metal. Sulfate-reducing bacteria are the most aggressive microbes. They can destroy an unprotected metal product in a short time unless electrochemical control measures are in place.
6. Other Corrosion Causes
Lesser known and rarer corrosion causes exist, too. One is high-temperature corrosion that happens where metal objects experience great heat continually. Jet engine exhaust ports are a prime example. Meta dusting is another corrosion cause. This occurs in high carbon and sulfuric gas situations where metal quickly corrodes from bulk to a fine powder. Weld decay and knifeline attacks also cause corrosion on metal fabricated equipment. Here, openings in seams allow ingress of corrosion-causing substances.
Corrosion is a natural process. Metal deterioration is inevitable and part of nature’s energy cycle. That’s unless metal manufacturers and maintainers take preventive steps to preserve their products.
How to Prevent Metal Corrosion
The key to preventing metal corrosion is to stop or slow the electrochemical forces that cause corrosion. Some metals are much more at-risk for corrosion than others. One of the main corrosion prevention factors is to choose a metal base that’s a low corrosion risk given its intended application and the environment it’s used in.
It’s also crucial to assess which corrosion causes a product may endure in order to prevent electrochemical breakdown. Above-ground applications have the highest atmospheric conditions that threaten a product. Generally, the best corrosion prevention is a top coating like paint or a baked-on powder. Below-ground applications also benefit from usable, but they usually need an anti-galvanizing treatment to stop electrical activity.
Metal corrosion may be inevitable given the right time and conditions. However, corrosion and engineering research has discovered short- and medium-term solutions to slow the kinetic process that causes corrosion and put the economic burden onto society. Here are the main types of corrosion prevention methods scientists and engineers work with:
Product Design: Scientists and engineers constantly thrive to improve existing technologies and design new corrosion-resistant metals. This includes developing advanced computer models that simulate actual conditions without the time and expense necessary to test products in real environments. Design work takes in accelerated testing in controlled conditions. Here, newly designed metal alloys provide the least corrosive metals. Plus, testing advanced coatings and finishes provides accurate performance predictions without the need for field tests.
Risk Mitigation: The same product design tools and databases allow metallurgists to mitigate the risk of product failure in real-time situations. Over the years, corrosion risk mitigation came from long-term study and experience of what metal alloys and protective coatings performed with the least corrosive action. Today, risk mitigation starts with applying the right corrosion resistant metals to their performance environment and then matching the correct protection in the way of coatings and electrochemical grounding.
Corrosion Detection: Metal scientists and structural engineers monitor existing products, buildings and infrastructure components to detect corrosion at different stages. Highly-technical sensors and remote monitors provide information on corrosive reactions that simply can’t be found by human sight and touch. Detecting metal corrosion plays a large part in prevention programs. Assessing current corrosion damage detected in existing materials provides a prognosis for predicting degradation and preventing serious failures.
Corrosion Prediction: Research and development, along with detection and mitigation techniques, allow scientific models to predict which metal products will withstand environmental forces. Scientific data also lets designers predict which materials are doomed for failure. Predictions based on metal properties extend into providing an accurate prescription of corrosion-resistant finishes and the successful way they can be applied to protect products. From information-based predictions, better materials and better protective coatings continue to evolve and make the world a safer place.
What Are the Most and Least Corrosive Metals?
True metals are rarely found in the earth’s mineral supply. Most true metals like gold, silver and platinum are non-corrosive by nature. They inherently resist corrosion and are in high demand, which is why they can be so expensive.
Other metals like copper, aluminum and brass also have excellent corrosion resistance properties. These materials are more abundant than precious metals and less costly by volume. The downside to brass, copper and aluminum is that they require considerable amounts of energy to process into usable products. That energy stores in their molecular makeup and makes them vulnerable to nature’s energy recycling program of electrochemical corrosion.
Copper is an interesting metal. It’s in relatively plentiful supply and is easy to work with. However, copper doesn’t need paint or powder coatings to preserve it from corrosion. When exposed to air and water, copper builds its own protection called passivation. Think of America’s famous landmark, the Statue of Liberty. Its copper sheathing has a rich greenish patina that naturally resists corrosion without other help.
Aluminum also forms a passivation protection layer. Without its greyish and mottled patina, shiny raw aluminum is somewhat corrosive. Boat builders often use aluminum for hulls and superstructures, which is partially because aluminum is lightweight and partially because it works well with products called sacrificial anodes. These small zinc or magnesium blocks or anodes absorb corrosive electrochemical reactions from aluminum and self-sacrifice by corroding first.
Because of corrosion threats, even resistant metals like aluminum often receive a surface protection coat. Many aluminum products destined for atmospheric exposure receive treatments during their manufacturing stage. Aluminum building products like siding and gutters have powder coats applied that last through years of harsh weather exposure.
Other metal alloys stand up well against corrosive conditions. Stainless steel is a blend of iron and chromium. As corrosion-resistant as stainless steel is, products manufactured from stainless steel often require protective coatings or regular anti-corrosion maintenance. Here is a list of common metals ranging from the most to least corrosive metals:
Magnesium and Alloys: Either cast or wrought
Zinc and Alloys: Wrought, die-cast or plated
Iron: Wrought, cast or carbon alloys
Steel: Refined iron and alloys like stainless steel
Aluminum: Smelted or cadmium plated
Lead: Solid or plated
Tin: Raw and lead-soldered
Chromium: Used to alloy stainless steel
Brass: Including bronze and alloys
Copper: Solid or plated
Nickel: Including titanium alloys
Silver: Solid or plated
Gold: Solid or plated
Platinum: Including gold-platinum alloys
Best Metals to Use
For most applications, you can use four reliable and economical metals. Each has distinct properties, and your metal choice depends on your specific application. That might be custom sheet metal fabricating, custom enclosure fabrication, steel fabrication or aluminum fabrication. No matter what your purpose, matching the best metal to use always includes providing it with the proper finish, such as powder coating.
Powder coating is an exceptionally dependable corrosion resistance process. This involves energizing a clean metal product and spraying a dry powder over it. The electrostatic reaction allows the powder to stick or adhere to the product. Following this, the metal product enters an over where it’s baked at 400 degrees Fahrenheit. Powder coated metal is one of the most cost-effective and long-lasting metal treatments available today.
APX York Sheet Metal provides first-rate metal fabrication and powder coating. Our services include product design, metal bending, metal rolling, laser cutting, machining, metal shearing and welding. Resisting corrosion is at the top of priorities at APX York Sheet Metal, which is why we always use these four best metals for building corrosion-resistant products:
Contact APX York Sheet Metal
We’re proud to be a leading custom metal fabricator in central Pennsylvania and northern Maryland. For more than 70 years, APX York Sheet Metal has built a reputation for excellence and dependability in both fabricating sheet metal and serving customers. As a valued customer, you’re faced with short lead times and rising costs. At APX York Sheet Metal, we understand that and strive to deliver low-cost value along with quick turnaround times.
Contact APX York Sheet Metal today for all your corrosion-resistant metal work. We’re just a call away at 717-767-2704, or you can always reach us online.