The process of machining materials to a net shape in an efficient and cost-effective way is an ongoing challenge for industries across the globe. The challenge is exacerbated when placed in the context of machining hard metals in a high labour cost country as seen within the EU. There are a number of factors that influence the cost of machining, one of the most easily influenced is that of tool wear.
In relation to tool wear, vibration is known to be a key factor driving premature failure. Industry has worked to address this by developing various tool holding technologies which have been shown to have a positive impact on tool wear. Due to the varying types and costs of tool holders, the challenge for companies is the selection of suitable tool holders which will guarantee an ROI.
In today’s machining environment we see a myriad of tool holder types and the price can vary from €45 up to €650 for a standard length tool holder. When selecting tool holders for a large machine tool with automation capability there typically be anything up to 180 tool holders the price difference becomes very relevant. Selection of tool holders is becoming more challenging for companies.
Tool holder Balancing
A noteworthy comment needs to be made with regards balancing of tool holders. As modern machine tools look to achieve higher spindle speeds and feedrates, the balance of the tool holder can play a big part on a number of factors including tool life, spindle life and part quality. The style of tool holder can play also play a significant part in the balance quality of the tool holder. Larger, heavier tool holders can be more difficult to balance but most tool holders are balanced by manufacturers and while this significantly improves the balance quality, when a cutting tool in introduced, these may need to be balanced together to give the best results.
Tool selection considerations
When selecting tool holders, one of the biggest factors to be considered is the material being machined. Harder materials will in most cases generate more vibration in the machining process and therefore tool holders with a higher damping effect should be considered. Softer materials may not generate the same forces but generally require higher spindle speeds.
Micro tools (less than 1mm) are generally run at very high spindle speeds therefore balance quality and tool run out would be tow of the biggest deciding factors. Higher MRR (Metal Removal Rates) regardless of the material type requires a more damping effect and greater clamping forces to prevent tool pull out.
Applications such as drilling and tapping may not require hydraulic or precision collet style toolholders and neither will general drilling applications but in both cases where high volume drilling/tapping with accurate carbide tools is being considered more accurate tool holders should be considered.
When looking to achieve higher accuracy levels and superior surface finishes, selection of the correct tool holder play an important part. Different tool holders can have different levels of run out effecting part quality. Tools with greater damping effect can improve tool surface finish.
Tool holders play a vital part in the cutting process and are often underestimated. In a lot of cases the cutting tool comes under scrutiny and companies will 3test new cutting tools to try increase tool life and reduce costs. If a typical cutting tool costs €100 but are using a €50 holder, it stands to reason that companies may not be getting full value from the cutting tool. An example is where an application uses 10 tools per shift on a €50 holder. A €100 holder might increase too life by only 10% but that means the application only used 9 tools per shift – immediately saving on tool cost. Very quickly a €500 tool holder does not look so expensive.
When trialling new cutting tools for their clients, vendors will ask firstly what holder is being used and if they can recommend an alternative, not just to sell a holder but to give the cutting tool the best opportunity to perform.
When selecting a tooling package for a highly automated machine tool with multiple holders, selection of each holder for each tool should be based on the application of that tool. ER collet chucks will work perfectly without effecting tool life on certain applications. It may be best to spread the overall cost of the tooling package across the selection – i.e.. higher quality tool holders where needed.