When a shop starts machining parts with an HMC, it changes workflows in various ways. Changing to an HMC also means modifying other processes, such as inspection and material loading/unloading.
One of the most obvious changes is shorter processing time per part. There are multiple reasons for this, including tombstone fixtures and a machine’s ability to pivot the workpiece with its B axis to reach different faces in one cycle.
High-Speed Machining
Using HSM on horizontal machining centers allows shops to shed pounds from the machining process, in the form of shorter cycle times that allow for more frequent production runs and that reduce inventory requirements that tie up capital. In addition, HSM enables more accurate work with cooler tooling and lower machining forces and vibration.
During the machining process, heat develops from friction and deformation of the metal as the cutting tool carves a chip from the green part. In high speed machining, the tool cuts so fast that it evacuates most of this heat with the chip rather than transferring it to the green workpiece. To do this, a machine must be designed to handle very high speeds, feeds and accelerations. That’s why Blair opted for a pair of HN63D machines, which are capable of running lights-out—unattended machining—for most of the shop’s milling operations. This lets the team run more frequent cycles and increase productivity without adding staff.
Three-Side Machining
When compared to VMCs, horizontal machines can offer much more productivity thanks to their multi-sided machining capabilities and natural chip flow. This translates into lower cycle times, less tool breakage and wear, greater part accuracy and more spindle ON time.
However, making the switch from vertical to horizontal can be tricky. Shop owners and general managers must evaluate whether the increased upfront cost is worth the faster cycle times, reduced tooling costs and greater part accuracy that are available with a horizontal machine.
Methods’ Meier notes that implementing a horizontal machine can be challenging for some job shops, particularly with respect to setting up the machine and programming probe cycles. But with a bit of patience and proper fixturing, it’s possible to quickly see a return on investment from the new technology. That, in turn, can lead to more business for the shop. This is why many companies consider switching to a horizontal machining centers in the first place.
Variable Spindle Speed
While it may not get as much attention as the VMC, a horizontal machining center offers a number of advantages that set this machine tool apart. These benefits include a highly precise open configuration and visibility, allowing operators to spot imperfections that they could otherwise miss and adjust operations accordingly.
Another benefit of HMCs is better chip evacuation compared to other types of mills, making this type of machine ideal for projects that require side-oriented work. Heavier and longer workpieces also lend themselves well to placing on a horizontal mill. In addition to increasing cycle times, unnecessary spindle range changes can place undue strain on the CNC system and even cause the machine to stall. A knowledgeable programmer will use the aforementioned variable speed feature to compensate, selecting lower ranges with ample power for rough machining and higher ranges for finishing. This reduces cycle time and prevents damage to the machine or tool. The varying speed also helps suppress chatter.