To extract the most from your tool and cutter grinder for carbide tool production, it’s vital that you are using the right wheels, that they are perfectly balanced and qualified and that you keep them in top condition throughout a complete batch.
So it all starts with wheel selection. Which wheels you select for each operation, can have a significant impact on tool quality, cycle time and the cost of your consumables. So choose your wheels carefully. Work closely with your wheel supplier to match wheel technologies to your application.
There are four basic criteria for selecting the perfect wheels for your application:
• Wheel size and shape
• Grit size
• Grit material
• Grit bonding method
Your wheel’s size and shape will be largely determined by your application requirements and the physical constraints of your tool grinder and process.
Choosing a grit size is relatively straight forward. Use coarser grit size for heavier applications such as fluting; a medium grit size for more general grinding and roughing operations such as back off grinding, some point grinding, gashing and some profiling. Select a finer grit wheel for finish grinding, profiling and smaller tools.
There are three grit materials commonly used in tool grinding. The hardest of these (Diamond) is the only grit type typically recommended for carbide grinding. The other common grit materials used in production grinding are Cubic Boron Nitride (CBN); which is often recommended for precision grinding of steels and Aluminium Oxide; which is softer than CBN but is easily dressed in process.
The three most common grit bonding systems are resin bond, metal bond and vitrified bond. Each bond has its advantages and disadvantages.
- Resin bonds are most common and are also the most flexible. They can provide a good balance between form holding and wheel breakdown.
- Metal bonds tend to be much harder, making in-process dressing more difficult, and are best used in profiling operations as they provide the best wheel shape retention.
- Vitrified bonds can be a lot softer and can lose wheel shape much easier, though this type of bond is the easiest to dress both in and out of process.
Recent grinding wheel technology has produced wheels with hybrid bonds. These wheels are best used for fluting as they provide much better wheel shape retention and thrive on deeper cuts with higher feedrates.
Preparing the wheel for grinding is very important when manufacturing carbide tools. Most wheels should be dressed from new once mounted on your wheel arbor. Dressing the wheel on the arbor you intend to use is best practice. This ensures concentricity, helps with wheel balance and will be a contributing factor towards tool finish, wheel life and ultimately efficient carbide tool production.
Once dressed, the wheel pack should be balanced. A balanced wheel pack avoids vibration and can contribute not only to improved tool finish, but also to extended wheel life, ultimately adding to your bottom line. Make sure you balance the wheel pack in the state it will be used on the machine.
There are many methods which can be used to balance your wheel packs. However, the most accurate technique is to utilise balancing assist software built directly into some advanced tool grinders. This type of software detects vibration patterns in a spinning spindle and tells you exactly where to install your balancing weights.
Conditioning your wheel (commonly known as white sticking) clears out accumulated debris built-up between the grits. White sticking your wheel in-between tools helps to reduce the load on your wheel. You want to keep your wheel cutting your tool, not just heating it up. So white sticking helps your wheel stay efficient in-between dressing cycles. This means that you can run with a higher feedrate and really load up your wheel, knowing that it is cutting true to form. Keep an eye on your spindle load meter for several tools so you can get a feel of how often to white stick your wheel. If your tool grinder has an automatic white sticking option, make sure you schedule this into the process periodically to keep your wheel cutting strong.
Depending on the type of wheel you have chosen, you may need to dress the wheel again during a batch if it dulls off too much or starts to lose shape. Advanced tool and cutter grinders often include in-process dressing abilities and you should schedule a dressing cycle after an appropriate number of tools if your wheel is of a dressable design. Ideally, your CNC tool grinder will automatically compensate for the slight change to the wheel diameter introduced by the dressing cycle.
Your wheel supplier should be able to give you the correct wheel speed for your wheel in RPM or surface speed. Feed rates will vary between different tools and operations. Optimal feed rate is a balance between wheel wear, spindle load, tool rigidity, finish, accuracy and cycle time. Your wheel supplier should be able to give you a starting point but you can gain significant improvements in cycle time or accuracy by optimising your feedrate to suit your specific application.