The most expensive mistakes with stamped metal parts don't occur in the press, but already in the design phase. Incorrect material selection, tolerances that don't match the material thickness, or a coating that hasn't been factored into the die calculation: these are common pitfalls with significant consequences for quality and cost. In this article, we discuss the most common material errors in stamping and how to prevent them.
Choosing materials based on end-use, not manufacturability
The most common mistake is selecting a material that perfectly fits the function of the final product, but doesn't align well with the stand process A drawing that is technically correct, but still leads to production failures, is a pattern that we at Eurotechniek regularly encounter. The cause is seldom in the geometry of the part, but more often in assumptions about material behaviour that do not align with the reality of production.
Stainless steel is a good example. It offers corrosion resistance and strength, and for applications in the food or medical sectors, that's entirely appropriate. However, stainless steel requires significantly more pressing force than cold-rolled steel, wears down tooling faster, and necessitates more precisely adjusted cutting clearances to prevent burrs. Anyone who doesn't factor this into the design phase will encounter issues during the first tooling test.
We also see this with aluminium. The material punches well and is light, but specific alloys such as series 5000 or 6000 behave differently during deep drawing than during flat stamping. A designer working with aluminium specifications from construction practice sometimes calculates with elongation values that are not representative for stamping. The result is a component that appears manufacturable on paper, but tears or exhibits a "feed" effect in the press.
Incorrect assumptions about material thickness and tolerances
A second recurring error is specifying tolerances that do not align with the chosen material thickness. For example, the drawing shows a length tolerance of plus or minus 0.03 mm on a 2 mm thick steel punched part. While theoretically achievable, this requires an additional calibration step after punching. Those who do not factor this step into time and cost will be in for a surprise when they receive the quote.
The rule of thumb is that achievable tolerance in punching is roughly one to two percent of the material thickness with standard die quality. With thinner material, below 0.8 mm, the absolute tolerance values are smaller, but the required die precision increases. At Eurotechniek, we always set the cutting clearance based on the specific material and the required dimensional accuracy. This may sound obvious, but it presupposes that this information is already available in the design phase. If the material choice is only finalised late, die development will be delayed.
Overlooking band steel and material availability
Stamping works most efficiently with strip steel: a continuous material strip that is automatically fed through the press. Not all materials are available as strip in the desired thickness and width. Special steels, less common alloys, or materials with specific surface treatments sometimes have to be supplied from plate and then cut. This entails additional handling and increases the material cost per part.
A practical example: a customer specified a particular spring steel alloy for an electrical contact. That alloy was only available in plate form. Cutting it to strip size added costs and introduced extra tolerances on the strip width. Ultimately, in consultation, a standard spring steel was chosen that was available in strip form and delivered technically equivalent performance. Die development could then commence without delay.
Surface condition and coating to be ignored as process parameter
Material does not always enter the press in an untreated state. Pre-treated strip steel, such as electro-galvanised or hot-dip galvanised material, is popular because it eliminates a post-treatment step. However, a zinc coating changes the effective material thickness and influences the cutting clearance required for a clean cut edge. Those who do not factor this coating into die clearance calculations will experience inaccurate cut edges or increased wear on the punches.
The same applies to materials with a mill scale or oxide layer. Bright steel that has been stored for a period before processing may exhibit surface oxidation, which affects lubrication and cutting resistance. We recommend that for pre-treated material, the nominal coating thickness should always be included in the specification program, so that the die is set up for it from the outset. A mismatch between coating thickness and cutting clearance is one of the hidden sources of error in a stamping process, as the effect builds up gradually rather than being immediately visible.
Underestimating material variation within a specification
A material specification on a drawing is a boundary, not an absolute value. Steel that complies with S235 can vary within that standard in yield strength, tensile strength, and elongation. At low volumes, this is hardly noticeable. At high volumes, especially with production in multiple batches or with changes in supplier, this variation can lead to inconsistent behaviour in the press.
We see this most clearly with spring steel and high-quality cold-rolled steel. The hardness class stated on the certificate covers a range. A die optimised for the middle of that range will perform differently with material from the upper limit. For long-term series, Eurotechniek structurally requests material certificates and monitors incoming material quality. This is not an unnecessary luxury, but a part of process control.
Material choice not aligned with desired post-treatment
Standard parts are rarely supplied in an untreated state. Galvanising, powder coating, anodising or passivation are common post-treatments. These treatments place demands on the base material. Aluminium that is anodised requires an alloy with a low copper content for a uniform anodising result. Steel that is powder coated must be free of heavy oxidation and sufficiently rough for adhesion.
One error we encounter is that post-treatment is planned, but not included in the material specification. The part is then stamped from a material that technically meets the functional requirements, but exhibits an irregular surface or a different colour after post-treatment. This error is only visible at the end of the production process, which makes recovery costs high. Specifying material and post-treatment in conjunction prevents this situation.
Frequently asked questions about material defects in stamped metal parts
How early in the design process should material selection be finalised?
Preferably at the start of mould development. The mould is adjusted to the specific material: thickness, hardness, coating and cutting behaviour. A material choice that changes halfway through tool development almost always leads to adjustments to the tool and delays the ramp-up phase. We discuss material choice as standard at Eurotechniek during the quotation phase, so that the mould is designed with the correct parameters from the outset.
What is the effect of incorrect cutting clearance on the parts?
Excessive clearance leads to ragged cut edges and dominance of the fracture zone. Insufficient clearance results in increased friction, higher punch loads, and accelerated wear. Both situations lead to dimensional deviations and increased rejection rates. The correct clearance depends on material thickness, material type, and the desired edge geometry. This combination varies per component and cannot be applied generically.
Can a material defect in the design be corrected later without a new mould?
Sometimes, but there is limited scope. Hardness and mirroring adjustments to the die can compensate for minor material quality variations. A fundamentally different material choice, with a different thickness or mechanical properties, usually requires adjustment of the cutting clearance or even a new die. The greater the deviation from the original material, the greater the tooling intervention required.
Preventing material defects is more worthwhile than correcting them
A material choice that is well-founded early in the design process will offer a structural advantage at the end of the production chain. Reduced mould wear, fewer rejects, shorter lead times and a more predictable cost per component are the direct consequences. Here at Eurotechniek, we are happy to contribute to material choices, tolerance setting and post-treatment right from the design phase.
A focused technical discussion before the tool goes into development prevents the most costly mistakes. Get in touch and explain your situation.