Sam MatsumotoClick image to enlargeby Sam Matsumoto

Selecting the right drill for stainless steel and titanium

Stainless steel and titanium are durable and corrosion resistant materials, so they are used in a wide variety of industries ranging from aerospace, medical and food to construction and architecture, to name a few. Both materials exhibit excellent wear resistance properties, but this makes it challenging to machine them. To select the right drill for accuracy and efficiency, you have to understand the common problems that occur when machining these materials before you can find solutions to overcome these problems.

Here are four common problems when machining stainless steel and titanium and a guideline on what you can do to eliminate the problems.

What makes stainless steel and titanium so difficult to machine?

Four common problems associated with machining stainless steel and titanium are work hardening, poor thermal conductivity, welding, and the elongation of chips.

1. Work hardening
Work hardening is the strengthening of a metal caused by plastic deformation. Non-brittle metals with high melting points, such as stainless steel, are prone to this condition. The keys to reducing plastic deformation are to minimize the cutting force against the work material and to maintain a sharp cutting edge.

The benefit of reducing work hardening in the drilling process is that it will contribute to prolonging the tool life for post-processing operations such as reaming and tapping.

Typical features to consider when selecting a drill.Click image to enlarge2. Poor thermal conductivity
Materials with poor thermal conductivity have difficulties in dispersing heat generated by machining.

The rise in overall cutting heat temperature can cause the tool substrate and the coating to oxidize, which accelerates tool wear. To suppress heat generation caused by friction, a drill designed with a sharp cutting edge, strong back taper, and thin margin area are essential. Furthermore, to quickly disperse machining heat, select a drill with coolant through capabilities.

3. Welding
Stainless steel has a high affinity with carbide materials making it highly susceptible to welding on the cutting tool and causing damage to it. To prevent this condition, a coating with a low coefficient of friction is recommended.

Chip shape comparison using CAE.Click image to enlarge4. Elongation of chips
High tensile strength is one of the unique characteristics of stainless steel and titanium. When machining these materials, the chips produced have a high tendency to elongate, causing chip packing issues. With drilling, it is very difficult to analyze the actual chip formation within the hole. To overcome this challenge, engineers have turned to computer aided engineering (CAE) technology for simulation, validation and optimization of products and manufacturing. With CAE, engineers are now able to examine the environment accurately and efficiently within the hole in order to develop the ideal point geometry for creating ideal compact chips. SMT

 

Sam Matsumoto is an application engineer with OSG in Canada.

 

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