Why Your Next VMC Should Be an HMC

I am often asked how to determine whether a vertical machining center or a horizontal machining center is most appropriate for a given part or job. In truth, the answer varies, depending upon the part being cut, the requirements of the set-up and changeovers, and even the other jobs being cut in the shop. In general however, I urge manufacturers to at least consider horizontal machining centers, even for mold and die work, and even considering that typical CNC horizontal machining centers are more expensive (at the time of purchase) than CNC vertical machining centers.

The reasons for my recommendation include:

• HMC spindle utilization averages are considerably higher than VMC spindle utilization averages
• Operator intervention is reduced on an HMC
• One HMC can often perform the same amount of work as multiple VMCs
• HMC capabilities now include milling and turning

Higher Spindle Utilization

American Machinist and University of Michigan surveys have shown that the average spindle utilization of a horizontal machining center is 85% and the average for a vertical machining center is 25%. This is a HUGE difference. If you consider that in an 8-hour shift, this means the HMC cuts for 6.8 hours and the VMC cuts for 2 hours, over the course of a week (for one shift), you get 24 extra hours of cutting time. That’s money in your pocket.

Reduced Operator Intervention

For a 6-sided part, production on a VMC requires the operator to move the part a minimum of 7 times, and without additional automation, the spindle is not cutting while the part is being moved. On an HMC, the maximum times the part needs to be moved is 3 and because HMCs typically have a pallet changer, the refixturing can be completed while the spindle is cutting (a second part).

Not only does the decreased operator intervention for a horizontal machining center increase spindle utilization (productivity), there is reduced opportunity for quality problems resulting from part handling.

Reduced Machine Requirements

Because part movement is reduced and spindle utilization is greatly increased with a horizontal machining center versus a vertical machining center, one HMC can perform the work of multiple VMCs. This reduces the number of machines required, thereby reducing the amount of floor space needed to house the machines. This also reduces the number of operators needed to run machines and reduces the amount of work-in-process necessary to keep the operation running. All these reduce the overall manufacturing costs and capital investment necessary for ongoing operation, thus increasing profitability.

Turning on a Horizontal Machining Center

Technology improvements now include the ability to perform Turn-Cut operations on a CNC horizontal machining center, something vertical machining centers are not capable of doing. Turn-Cut is a new process that allows the part to remain fixed (on a tombstone) while the spindle performs turning operations such as threading and ID/OD cutting. This is possible without the additional investment of special tooling, chucks and fixtures. With a vertical machining center, the part would need to be moved to a lathe to perform turning operations, again, increasing part movement, operator intervention and the possibility of quality problems.

While a horizontal machining center might not be the right choice for every part, there are compelling productivity, cost and quality reasons to at least consider an HMC where you might have initially thought a VMC would be the machine of choice. Without a thorough review of the options, you might not realize the level of productivity you can achieve.

Got questions about whether a VMC or HMC is right for you? Comment below, or contact us and we’ll help you evaluate your options.

Jim Endsley is Machining Center Product Specialist, Okuma America Corporation.