Page 61 - MetalForming May 2012

to create a superior surface finish. Those seeking a porous finish would not require a wiper insert.
If hard milling is an entirely new approach for a manufacturer, the company should seek an OEM partner that specializes in hard-milling tools. Such a partner can assist in cutting- tool selection, as well as offer a cutting strategy that includes proper setting of feeds and speeds, depths of cut and programming. After all, hard milling differs significantly from con- ventional milling, and proper know- how is vital to successful implemen- tation, future gains in productivity and profitability.
When preparing to conduct a milling test—in light of the high upfront costs associated with CBN—manufac- turers should take steps to ensure they don’t invest a significant amount of money during the evaluation. For example, the test cutter need not have every pocket loaded with CBN. An effective test can occur with only one or
two inserts and an adequately adjust- ed feed rate.
Proper Technique
If after much consideration a man- ufacturer decides to invest in the hard- milling process using CBN, it should keep two very important things in mind. First, while conventional machining processes apply coolant to help disperse heat and effectively remove chips, a manufacturer using CBN to hard mill should avoid the use of coolant. CBN generates excessive heat at the cutting zone, and as heat transfers to the chips the coolant vapor- izes on contact. Further, coolant can create instability in the tool since milling involves interrupted cuts—the CBN insert is out of the cut 50 percent of the time, so it’s constantly heating up and cooling down. Adding coolant to the process would cause the insert to go into thermal shock. To displace chips, die shops can use compressed air.
In addition, operators will often mis-
takenly program the milling machine for climb cutting during hard milling. During climb cutting, the width of the cut starts at the maximum and decreas- es to zero. While climb cutting is the correct technique for milling with car- bide and high-speed steel cutters, oper- ators should avoid this method when hard milling with CBN, as it is detri- mental to tool life. Climb cutting grabs a thick chip and thins it out during the cut. With CBN, rather than grabbing a thick chunk of steel and slamming into the side of a part, optimum results come from easing into the material and producing a larger chip as the cut- ter exits the part.
While change can be scary, manu- facturers that currently perform a lot of grinding and post-heat treatment oper- ations should consider hard milling— it’s faster and less costly. Sure there are still some unknowns, but with the right OEM support and a clear understand- ing of what goes into the process, any- one can be successful. MF
Tooling Technology
THE FIRST NAME IN QUALITY BLANKING
What’s made Toledo Blank a trusted source for blanking since 1974? Lean, low-cost manufacturing processes. An on-site die shop, first operation blanking sales and processing services. All resulting in cost-effective options to help minimize scrap and freight costs.
We Offer...
Sales and processing programs
JIT Inventory
Strategic location near steel producers and processors.
Find out more about how Toledo Blank can help your bottom line.
TOLEDO BLANK
135 N. FEARING BLVD.
TOLEDO, OH 43607 WWW.HEIDTMAN.COM/TOLEDOBLANK MATT.MCCAFFERY@HEIDTMAN.COM 419-385-0636
www.metalformingmagazine.com
MetalForming/May 2012 59