M2 is a widely used molybdenum high-speed-steel grade with a practical balance of wear resistance, toughness, grindability and cost. It is commonly considered for general punching applications, but suitability still depends on work material, thickness, geometry, clearance, production volume and heat treatment.
M35 is a cobalt-alloyed HSS grade. Official Erasteel information describes cobalt as improving hot hardness while maintaining a useful balance of toughness and hardness. For punching, it may be considered where higher thermal and wear demands exist, subject to geometry, shock and heat-treatment review.
M42 is a higher-cobalt HSS grade associated with high hot hardness and wear resistance. It can be useful in demanding cutting applications but may require more careful control of toughness, grinding and shock. Selection for a punch should consider point size, work material, alignment and production duty.
The live page states 64 ± 2 HRC. This should be treated as a quoted product range, not a universal value for every grade, diameter or head style. Buyers should request the final working hardness, test method, heat-treatment condition and acceptable hardness zones.
Not always. Standard punch manufacturers may specify a harder shaft or cutting section and a tougher, lower-hardness head to reduce head fracture. The correct hardness profile depends on punch design and manufacturing route. Vardhman should publish point, shaft and head hardness separately when applicable.
This specification denotes the Ra surface roughness in micrometers. Precision grinding and micro-polishing down to Ra 0.04–0.3 µm lowers piercing friction, reduces adhesive galling, and ensures clean part edge quality.
High concentricity between the shank and the cutting point (typically within 0.005 mm) ensures even clearance around the entire perimeter of the mating die, preventing one-sided burrs and premature tool chipping.
Sharp corners create severe stress concentrations under cyclic impact. Generous ground transition radii between the shank, point, and head prevent fatigue cracks and head breakage.
Standard configurations include ISO/DIN straight shanks, headed punches (conical head, 30° head, 60° head, shoulder head), ball-lock quick-change retainers, and key-flatted anti-rotation shanks for shaped punches.
Total clearance is calculated as a percentage of stock thickness per side (typically 5% to 12% depending on material tensile strength, hardness, and desired cut-band-to-breakout ratio).
Excessive secondary shear creates extreme cutting pressures, generating heat, accelerated edge wear, severe stripping forces, and rapid cutting-edge chipping.
Excessive clearance results in large, sharp burrs on the workpiece, excessive edge rollover, dimensional hole distortion, and frequent slug pulling into the die.
Close-fitting guide bushings in the stripper plate support small-diameter or slender punches close to the stock surface, preventing column buckling and vibration under compressive loads.
Sheet material elastic spring-back tightly grips the punch point. Rough land finishes, lack of lubrication, insufficient back taper, or tight die clearances increase stripping friction.
Edge chipping results from improper die clearance, press misalignment, ram tipping, high stock hardness, thermal shock during grinding, or choosing an overly brittle hardness level.
Breakage is triggered by stock misfeeds, double blanking, severe side loading, loose retainer mounting, inadequate shank support, or excessive unsupported length-to-diameter ratio.
Head failures occur when retainer counterbores are un-chamfered or uneven, backing plates are too soft, high stripping tension pulls on the head, or the head was over-hardened.
Uneven wear indicates non-parallel press strokes, misalignment between punch and die holders, unbalanced shear loads, or uneven stripper clamping pressure.
Frictional heat and pressure cause soft metals (aluminium, brass, soft stainless) to adhere to steel punch walls. Lapping, PVD coatings (such as DLC or CrN), and extreme-pressure lubricants stop galling.
While geometrically possible, cutting clearance, surface finish, shear profile, and lubrication requirements differ drastically across material types. Tool parameters must be optimized for each alloy.
Use cobalt HSS grades (M35 or M42) or PM-HSS, increase die clearance (10–14%), apply shear angles to reduce snap-through tonnage shock, and apply TiAlN or AlCrN coatings.
Yes. Rooftop, concave, or single-bevel shear angles stagger the cutting contact through the stroke, reducing peak punching force and press shock loads by up to 30–50%.
Piercing Force = Perimeter (π × d for round) × Stock Thickness × Material Shear Strength. Include a safety factor of 20–30% to account for punch dulling and stripper load.
Sharpen as soon as a 0.05–0.10 mm edge wear land or noticeable part burr appears. Routine maintenance removes minimal stock and prevents deep corner micro-cracking.
Use sharp CBN (cubic boron nitride) grinding wheels with continuous flood coolant, light depth of cut passes, and regular wheel dressing to avoid burning or softening the cutting edge.
Fit spring-loaded mechanical slug ejector pins in the punch face, add shear angles, apply vacuum relief holes, or use engineered slug-hugger die buttons.
Stainless steel work-hardens rapidly and generates high stripping friction. Ensure tight alignment, generous die clearance (9–12%), high-pressure lubricant, and TiCN or TiAlN coated punches.
Softer and more adhesive metals can build up on the punch and may require different clearance, polished relief, back taper, coating and lubricant. Surface cleanliness matters for cosmetic parts. Share the alloy, temper, thickness, finish requirement and downstream cleaning or joining process.
The page lists diameters down to 0.2 mm, subject to confirmation. Feasibility depends on sheet thickness and strength, unsupported punch length, guidance, clearance, stripper design, press alignment and slug removal. A small diameter alone does not guarantee a workable production tool.
