The main causes of metal working distortion and how to solve it

old sledgehammer standing in garageold sledgehammer standing in garage

Do you have a current problem with sheet metal distortion? Are you wondering what the most effective and commercially viable solutions are to the problem? The answer is not a sledgehammer, although it is surprising the number of customers we see still using a sledgehammer to flatten out metal!

In this blog we have identified the main causes of sheet metal distortion and the most common solutions available today, suitable for every budget.

The Main Causes of Sheet Metal and Metal Plate Distortion

There are several different causes of distortion, largely involving temperature and force. Distortion results from introduction or release of localised internal stress within the material, for instances, welded metal expanding or contracting in relation to the base metal. The physical and mechanical properties of the metal (including its yield strength, elasticity, and thermal expansion) change during both heating and cooling cycles, and may not return to the original condition afterwards.

Flame, laser or plasma cutting and hole-punching are two of the most common causes of metal distortion in any metal working procedure:

Flame Cutting

By their nature, laser, plasma and flame-cutting can result in heat distortion due to the transfer of heat into the material. If minimising heat input is critical to your application, consider waterjet cutting which eliminates any heat distortion.

Punching Holes

Hole-punching through metal sheet or plate also leads to distortion, particularly when the holes are close together. This is because the exit side of the material is stretched when the punch pushes through the material to make the hole. Some of the energy used in pushing the plug through the material transfers the material sideways, resulting in the exit side expanding relative to the top side.

Engineering Solutions for Every Budget

If these sound like familiar issues, then the good news is that there are plenty of solutions readily available on the market. Some of these solutions involve sourcing simple and budget-friendly pieces of new machinery. Other solutions come at a premium cost and require a full redesign of your shop floor’s workflow.

The most trusted solution is, unsurprisingly, the most expensive one: the best way to remove heat distortion quickly and efficiently is to install a dedicated straightening machine. These machines operate with numerical control (NC), or computer numerical control (CNC). The machine will automatically read the distortion in the material, adjust the position and force applied by a series of rollers through which the material passes and delivers a perfectly flat sheet, often in one pass.

There are many different types of straightening machines, but each of them is specifically designed to smooth out any distortion by using rollers. These are significant machines and a premium purchase – you can expect a single machine to cost a six figure-sum.

That being said, the best solution is the one that best suits your business; not everyone needs a dedicated straightening machine. Thankfully, for both forms of distortion, there are other less expensive pieces of machinery that will still flatten sheet effectively, at just a fraction of the cost.

Sheet Rolls

Sheets Rolls are suitable for flattening large sheets which have been distorted. Passing distorted material through these rolls in different orientations is most effective and turning the sheet over can also help.

Sheet rolls can also do small flats and solids on the profile section of the rolls. In this case, the machine is economical, however, there are the added costs and risks of multiple sheet manipulations to consider as well; especially if the sheet has to be turned over between passes.

Section Rolls

Section Rolls are fitted as standard with easily adaptable tooling for multiple different material types / profiles. Section rolls can handle flat, solid bar, angle, box section and channel. Both manual and hydraulic machines will do the job, and bespoke tooling can even be designed and produced for work on more challenging / technical applications.

That being said, these machines require experience and skill on the part of the user to effectively remove distortion.

H-Frame Press

H-Frame Presses can be fitted with a bar-straightener tool. The benefit of this machine is its flexibility as it can be set-up with a wide range of different tooling options for different profiles, sheets, etc. It can also be used as a basic press brake with the correct tooling.

Horizontal Bending Press

Another great option to help remove heat distortion is the Horizontal Bending Press, which can also be fitted with a bar straightener.

These machines are easily programmable to produce repeat results. Depending on the tonnage / capacity of your machine this is ideal for narrow profiles. A range of common tooling for the Horizontal Bending Press can be viewed here.

Engineering Solutions for Hole-Punching

If you have a current issue with distortion from punching plate, there are a few low cost options which can make a significant difference:

Check Your Punching Clearance

The first thing to check is that you have optimum punching clearance on your die. By reducing the clearance, you will focus the pressure on the material more centrally and this will result in a cleaner punch through the material.

Adjust the Stripper

Ensuring the stripper assembly is correctly adjusted so it just “kisses” the material is key to minimising deformation. In some applications you will be able to turn the material over between each punch so that it is punched from either side alternately, sharing the distortion out between both sides of the bar.

What About a Minimum Deform Stripper?

For a steelworker, a minimum deform stripper assembly can also be used. Neoprene ball-springs maintain the downward force of the stripper either side of material, whilst the punch is withdrawn. This, again, helps to minimise material distortion – Please note that this solution is only for mild steel up to 10mm thick.

For more information on sheet metal distortion or to discuss your options, please get in touch.

Published 16th February 2021