M2 is a widely used molybdenum high-speed steel. M35 and M42 are cobalt-bearing HSS grades developed for greater hot hardness and wear resistance, with trade-offs in cost and toughness. Final selection depends on work material, thickness, speed, geometry, shock, lubrication and the supplier's heat treatment.
The live Carbide Punches page lists HSS M2, M42 and M35 and 64 ± 2 HRC, which conflicts with the product name. Buyers should request the actual carbide grade, cobalt binder, hardness scale, HIP status, toughness, point finish and recommended application before approval.
An HSS block punch is a larger-section or non-standard shaped punch manufactured as a block component rather than a simple round-shank punch. It may create rectangular, slot or complex profiles. Drawing details must include profile, orientation, head or mounting, length, radii, material, hardness and tolerance.
An HSS step punch has two or more controlled diameters or profiles along its working section. Steps may provide guidance, relief, staged engagement or a special hole form. The drawing should define every diameter or width, step length, transition radius, point geometry, orientation, material and hardness.
A D-shape punch creates a profile with a curved portion and one flat side. It requires orientation control so the flat remains aligned with the die opening. Specify the diameter or curved size, flat position, keying, head or retainer, corner transition, length, material, hardness and tolerance.
Specify the square dimensions, corner radii, orientation, cutting clearance, point length, shank, head or retainer, overall length, material, hardness, coating and tolerance. The current Vardhman square-punch page uses a generic diameter field, which should be replaced with shape-specific dimensions.
A pilot punch enters a previously pierced pilot hole to locate the strip accurately before subsequent operations. It helps control pitch and registration but should not carry the main feed load. Tip form, lead, diameter, mounting, material and spring-loaded or fixed design depend on the strip and die sequence.
Clearance is the gap between the punch cutting edge and the die opening. Correct clearance helps control fracture, burr, hole geometry, stripping force, punch load, slug behaviour and tool life. It should be selected from the sheet material, thickness, strength, required edge quality and tooling condition.
Excessively tight clearance can increase cutting and stripping force, heat, secondary shear, abrasive wear, chipping, slug jamming and press load. It may produce a larger burnished land but not necessarily the best tool life. The correct value must be engineered for the actual material and thickness.
Excessive clearance can increase rollover, taper, burr or edge distortion and may reduce dimensional control. It can also affect slug size and retention. The acceptable clearance depends on whether edge quality, burr direction, press load, tool life or downstream forming is the priority.
Burr can increase because of worn or chipped edges, unsuitable clearance, poor alignment, loose tooling, excessive punch entry, sheet variation, damaged die buttons or incorrect material control. Inspect the burr direction and the punch, die and stripper before deciding whether to sharpen or change clearance.
Rollover is the initial rounded deformation at punch entry. Burnished land is the smoother sheared portion produced during penetration. Fracture is the rougher breakaway zone where cracks meet. Their proportions are influenced by material, thickness, clearance, edge sharpness and tool alignment.
Slug pulling occurs when the slug sticks to the punch face and is drawn upward instead of falling through the die. Causes can include vacuum, lubricant, magnetism, poor slug retention, unsuitable clearance, worn tooling or punch-face condition. The remedy must match the actual die and material.
Slug jamming can result from tight clearance, insufficient relief, poor die taper, burr accumulation, double slugs, misalignment, damaged die buttons or inadequate slug escape. Inspect and clean the slug path before production resumes; forcing the press can break the punch or damage the die.
After cutting, the sheet grips the punch and the stripper must remove it during return. High stripping force increases tension, bending and head or retainer load. Clearance, work material, lubrication, point finish, punch entry, hole size and stripper design all influence the force.
Breakage can result from misalignment, side load, inadequate guidance, excessive unsupported length, wrong clearance, high stripping force, poor material control, unsuitable steel or heat treatment, over-entry, damaged retainers, press deflection or sharp stress concentrations. The root cause should be corrected before fitting a new punch.
Chipping is often caused by local impact, tight clearance, brittle material or heat treatment, misalignment, insufficient edge support, sharp profile corners, slug interference or inappropriate coating. Examine the fracture location and die condition to distinguish impact chipping from progressive wear.
A small punch behaves like a slender column. Excess unsupported length, side load, off-centre stripping, poor guidance, feed error, misalignment and high force can cause bending. Increase guidance, reduce unsupported length and confirm material, clearance and punch design rather than only selecting a harder grade.
Galling is adhesive transfer of work material to the punch surface. It is promoted by friction, heat, poor lubrication, incompatible material pairs, rough finish, high contact pressure and incorrect clearance. Polishing or coating can help, but the process, lubricant and die design must also be corrected.
Abrasive work materials, scale, coatings, hard inclusions, tight clearance, high production volume, unsuitable tool steel, insufficient hardness and poor lubrication can accelerate wear. Inspect both punch and die because a worn die opening can continue damaging a replacement punch.
A smooth working surface can reduce friction, material pickup and stripping force, while the cutting edge must retain the intended sharp geometry. Vardhman child pages list 0.3 to 0.04 micron without identifying the parameter or surface. Request a drawing that specifies Ra or other finish by feature.
No. The required hardness depends on material grade, toughness, punch size, shape, head design, work material, shock and heat treatment. Vardhman repeats 64 ± 2 HRC on many child pages, but carbide and some headed or complex punches need different specification methods and hardness zones.
Small-hole punching requires careful control of punch diameter, unsupported length, guidance, clearance, stripping, work-material strength, press alignment and slug removal. Avoid applying one diameter-to-thickness rule universally. Share the material, thickness, hole size, tolerance and production volume for engineering review.
Higher-strength materials increase cutting load, stripping force and risk of chipping, galling and punch-head failure. Tool steel, head design, clearance, coating, guidance, lubricant and press rigidity may need changes. Use verified material strength and thickness rather than applying mild-steel settings.
The same basic geometry may not perform equally across all materials. Strength, ductility, abrasiveness, galling tendency, springback and burr requirements affect clearance, tool material, coating, lubricant and edge preparation. Specify the exact alloy, condition and thickness for every application.
A suitable lubricant can reduce friction, heat, galling and stripping force and may extend punch and die life. It must be compatible with the sheet material, coating, downstream cleaning or welding and workplace requirements. Too much or unsuitable lubricant can worsen slug-pulling or contamination problems.
Sharpen when burr, edge condition, hole quality, press load or inspection records show progressive wear. Do not wait for severe chipping or breakage. Regrinding must restore the correct face, shear and edge geometry, and the die opening, clearance and alignment should be checked at the same time.
