Choosing the right insert geometry and grade for an application can easily make or break a job. Making the right choice requires educating yourself on what types of cutting edge and carbide grades are best suited to the machining conditions present. Typical considerations include:
Other factors can come into play, but those listed above are almost always the important issues when determining what geometry and grade to select. Following are some brief suggestions for geometry and grade selection, according to the variables above.
Keep in mind that these are typical scenarios and this selection process will in most cases result in the correct choice. However, combinations of the above factors can create unique situations that call for unusual grade/geometry selections. The best course of action is to contact your Dapra Applications Specialist for technical support. We are here to help!
Dapra uses an easy-to-understand system that separates grades by toughness/hardness. The same coatings are available for each carbide substrate, so choosing the grade begins with the toughness of the substrate desired and ends with the coating of choice.
For abusive applications, use of the toughest grade is recommended. These would be identified as the following: interrupted cuts; long tool lengths; poor chip evacuation; stainless steels; high-temperature alloys; poor workpiece or machine rigidity; coolant use or very heavy cut depths.
These abusive applications require a cutting tool with high shock resistance and toughness to reduce the chance of insert chipping. Use of these grades will provide excellent toughness at the cost of some wear resistance properties.
Dapra's toughest (most shock-resistant) Square Shoulder insert grades are:
For stable, steel and ductile iron applications, Dapra recommends our medium toughness/hardness carbide. Examples of some good applications include: uninterrupted steel cuts; good workholding / machine rigidity; short tool / diameter ratios; lighter depths of cut; good chip evacuation; alloys; low and high carbon steels; ductile (long-chipping) irons; and dry machining.
Dapra's mid grade provides high performance and increased tool life over the toughest grade, due to increased hardness of the carbide substrate. This allows higher speed and improved wear resistance, but at a slightly higher risk of insert chipping.
Available grades include:
For very stable, high-wear applications in cast iron and nonferrous materials, as well as hard milling of heat-treated materials, Dapra recommends the use of our hardest grades. Application examples include: gray cast irons; aluminum and copper alloys; plastics; light, smooth cuts in any material; and heat-treated steels (typically over 48 Rc).
Dapra's hardest grades provide optimum wear resistance, with the longest tool life possible. However, insert chipping is a more common occurrence when shock is encountered. Dapra's hardest grades are:
Dapra offers three different cutting edges for the Square Shoulder milling line:
APET – Strong reinforced cutting edge for optimum wear and chip resistance. This geometry will provide the strongest edge, but at increased spindle load and usually higher decibel levels.
XPET – Sharper edge for cutting gummier materials such as low carbon steel, stainless steel and high-temperature alloys. Light hone provides some reinforcement and reduces cutting forces and noise. More susceptible to edge chipping.
XPET-ALU – Sharpest edge. Ideal for aluminums and plastics where high-shear cutting is needed. Creates the lowest spindle load and least noise, but most susceptible to edge chipping.
The minimum FPT (feed per tooth) for the APET geometry should be .006". This is to get the chip thickness past the T-land edge preparation, allowing the insert to cut, not rub. The minimum FPT for the XPET insert should be .003". Consequently, lighter cuts (FPT) should not be taken with the APET unless other conditions exist that necessitate the use of the stronger edge.
The selection procedure described here will require your careful consideration of several application conditions and insert characteristics. This may take some time, but the cutting results will be well worth your effort.