Milling and turning

  • Use sharp, file-sharpened tool edges.
  • High cutting speed.
  • Slow feed rate.
  • Greater clearance than for metals.
  • Milling is difficult below 50 Shore A.
  • Cooling is recommended

Drilling

  • Use twist drills.
  • Sharp edges.
  • Clearance angle 0 or negative.
  • Point angle 90–110 for large diameters and/or thick-walled parts, 115–130 for thin-walled parts.
  • Slow feed (approx. 0.2 mm/rev).
  • High speed.
  • Cooling with cutting oil.

Drilling and punching

The drill should be retracted occasionally to prevent chips from blocking the hole. If a series of small holes is to be drilled, pins should be inserted into the finished holes; otherwise, the material “flows” into them and the new holes will not be round. Polyurethane is elastic and springs back. The hole will therefore be about 4% smaller than the drill bit. For making holes in thin sheets, punching can also be used. For this purpose, sharp hollow punches mounted in a press are used. Generally, holes larger than the thickness of the polyurethane are difficult to punch. In reality, it is the strength of the punching tool that is the limitation. When punching thick sheets, the hole becomes “hourglass-shaped.”

Splitting

A variety of methods exist for manufacturing thin sheets from thicker ones. Using so-called splitting machines, the most important part of which is a sharp knife, it is possible to manufacture very thin foils from a polyurethane cylinder. Thick sheets can also be sawn with a standard band saw. The material should then be cooled with a coolant.

Read more about polyurethane sheets here.

Bonding of polyurethane

It is easiest to achieve good adhesion if the polyurethane is not fully cured. If the polyurethane is fully cured, the surface must be roughened or blasted with steel grit. The surface must then be made very clean from dirt and release agents. A major problem is silicone oil-based release agents, which are difficult to remove completely.

For bonding polyurethanes, polyurethane adhesives or fairly flexible epoxy adhesives are best suited. The adhesive should provide a joint that has lower stiffness than the polyurethane; otherwise, there is a risk of the joint breaking under bending loads.