Choosing the Right Insert Dapra Grade & Geometry for Your Application

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.
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Typical considerations include:

• Material being machined
• Workholding rigidity
• Machine tool rigidity (40 or 50 taper, box or linear ways
• Tool holder used
• Tool length / diameter ratio
• Coolant vs. dry machining
• Machining parameters (DOC, WOC, speed & feed)

​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!

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Grade Selection

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.
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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:

• DMP35 (uncoated substrate – toughest grade)
• DMP35-GLH (medium to high temperatures in steels and irons)
• DMP35-HM (high temperatures in tough stainless steels, high-temp. alloys, titanium)
• DMK35 (uncoated substrate – tough grade – XPET only)
• DMK35-HM (high temperatures in tough stainless steels)
• DMK35-IN (premium high-temperature coating for high-temp. alloys, tough stainless steel, Inconel)

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.
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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:

• DMP30 (uncoated substrate – for most steels and ductile irons)
• DMP30-GLH (high temperatures – general alloy and mold steels)
• DMP30-HM (high temperatures in tool steels)
• DMK30 (uncoated substrate – for tough stainless steels, high-temp. alloys, irons)
• DMK30-GLH (medium to high temperatures)
• DMK30-HM (high temperatures in tough stainless steels)

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.

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Dapra's hardest grades are:

• DMK25 (uncoated substrate)
• DMK25-GLH (medium to high temperatures and hardness)
• DMK25-HM (highest temperatures & hardness – suitable for hardened steels and the best wear resistance in cast iron)

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Geometry Selection

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.

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General Recommendations

Material Being Machined
Use stronger, T-land cutting edges for steels and cast irons. Use sharper honed edges for stainless steels and high-temperature alloys. For aluminum and plastics, use sharp, un-honed cutting edges.

Workholding / Machine Tool Rigidity
Use the recommended grades and geometries for rigid setups and machines. In cases where rigidity is lacking (light-duty machine, poor workholding, etc.), use tougher grades and stronger geometries. The exception to this rule is when the use of the sharper geometry (XPET) actually stops or reduces the vibration created by the poor rigidity. These situations typically present a "trial and error” scenario.
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Material	Geometry Recommendation
Low carbon steels	XPET
Medium carbon, alloy steels	APET
Hardened steels	APET
Stainless steels	XPET
Cast irons	APET
Aluminums	XPET-ALU
Copper alloys	XPET
High-temperature alloys	XPET
Titanium	XPET
Plastics	XPET-ALU

Long Toolholder / Length to Diameter Ratio 
This situation closely resembles the previous rigidity issue. Long tool lengths (including longer tool holders) decrease tool rigidity, creating the potential for chatter and vibration. This can typically be combated with stronger cutting edges, but can also sometimes be corrected with a sharper, free cutting edge. Use the APET unless the results prohibit the use of such a strong edge. The XPET may reduce vibration enough to quiet the operation. Again, use of the toughest grades is typically recommended in long reach applications where chatter or vibration is present.

Coolant vs. Dry Machining
Most applications using Dapra cutting tools are best performed using dry air blast. Exceptions to this rule include: high-temperature alloys, aluminum and some exceptionally tough stainless steels. When dry machining, use the grades and geometries suggested previously. When using coolants, Dapra recommends using the tougher grades, but with sharper cutting edges (XPET). This allows the heat generated in the cutting zone to be minimized, delaying the effects of thermal shock.

Machining Parameters 
For heavier cuts, tougher substrates should be used, due to the increased pressure and potential vibration created. In lighter cuts, the harder grades provide better performance (speed) and longer tool life.

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.
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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.