Toolmaking
New design approach - additive manufacturing of milling cutters
Additive manufacturing enables new design freedoms away from the familiar. The example of a newly developed milling cutter concept shows how the advantages of the manufacturing process unfold in tool body development. By Thomas Wikgren
Additive manufacturing is forcing engineers to completely rethink their job. That may sound extreme, but if you look at the freedom that this fast-growing technology offers, it is very realistic.
What is exciting about the additive process is its transformative nature. Because "printing" or "adding" something instead of "subtracting" from a solid material means that internal structures can be produced with greater complexity. End products and components can thus be better optimized for their respective use. For example, it is possible to manufacture cutting tools with complex internal cavities and cooling channels - this reduces weight and increases performance. The same applies to many other metallic parts, allowing additive manufacturing to achieve unprecedented topology optimization. However, engineers have so far mainly learned to think and plan in terms of subtractive technologies. And it may take some time for this thinking to change and for science and industry to invest in the new technologies.
A mutually complementary process
When it comes to additive manufacturing, it is important to understand that it does not simply replace subtractive processes. Rather, additive manufacturing should be seen as a complementary technology that can be considered for certain applications.
So how can a company decide whether this process is suitable for them? A checklist is at least a good start: Does the component to be manufactured have a complex shape? Does the material required have a high price? And is low weight an important requirement of the component to be manufactured? If so, the component could be a candidate for additive manufacturing.
Other questions are: Is the component likely to be available in many different versions due to customized mass production? Is it possible to combine subcomponents into one component? Is it important to shorten assembly time and increase productivity or reduce stock levels? Again, if this is the case, additive manufacturing could be the solution.
The choice of the right powder also plays an important role, as its quality and properties have a strong influence on the properties of the component. Three main aspects need to be considered: the choice of raw material, the particle size and the morphology. There are currently five major alloy groups that are used in additive processes: Steel, cobalt-chromium, nickel, aluminum and titanium. As a manufacturer of metal powders for additive manufacturing, Sandvik offers a wide range of alloys - including customized materials.
Printing processes at a glance
All additive manufacturing processes are characterized by the layer-by-layer production of three-dimensional objects, but the production techniques differ. The printing processes can be classified either by their energy source or by the way in which the material is joined together - for example, by laser or binder. Sandvik has all the relevant printing processes for metal powder in-house.
Powder bed fusion uses either a laser or electron beam to melt and bond the powder. The process is repeated layer by layer until the last layer has melted and the components are complete. These are then removed from the build plate and reworked as required. Powder bed fusion processes are suitable for a wide range of materials and applications, as the parts generally have a high level of strength and there are numerous methods of post-processing.
The binder process uses a powder-based material and a mostly liquid binder that acts as an adhesive between the powder layers. A print head moves horizontally and alternately applies layers of the building material and the binder. After each layer, the object to be printed is lowered together with its building platform. The resulting object is in a green state and requires post-processing, where the green body is cured in an oven to remove the solvent from the binder. Finally, the part is debinded and sintered to almost complete density in a sintering furnace.
In order to achieve the right characteristics such as surface quality, geo-metric accuracy and mechanical properties, almost all additively manufactured components require some form of post-processing. For example, heat treatment, separation of the component from the supporting structure and the building panel, machining, surface treatment, testing and certification.
Meanwhile, internal surfaces, such as internal cooling channels, can be polished using abrasive flow machining.
Additive manufacturing as an enabling technology
Knowledge along the value chain - from topology and powder to manufacturing and post-processing - has enabled Sandvik Coromant to launch its first additively manufactured tool body. The Coro Mill 390 Light Weight is an example of how this process can be used in combination with optimized material selection to create complex shapes and internal part features. In this case, a tool was realized that is 80 percent lighter than subtractive methods would allow. This enables a more compact design which, in combination with a Silent Tools milling adapter, reduces the distance between the damper and the cutting edge and improves process reliability when milling with long overlengths.
The tool design is the result of numerous passes. Different topologies and materials - ultimately switching from a steel alloy to a titanium alloy - could be produced quickly using the powder bed fusion process, reducing the weight to a minimum. Overall, we are all at the beginning of an exciting development as we learn to design and manufacture products in a completely new way. But it will never be technology for technology's sake. Rather, with each new step, Sandvik Coromant will also ask itself how additive manufacturing can create added value for its customers. And where it doesn't make sense, it won't pursue it.
Additive manufacturing will certainly lead to new types of products that we can't even imagine today. This promises a really exciting future for companies.
The author:
Thomas Wikgren, Manager Product Application Management at Sandvik Coromant
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