Modern Machine Shop is focused on all aspects of metalworking technology - Providing the new product technologies; process solutions; supplier listings; business management; networking; and event information that companies need to be competitive.
Issue link: https://mms.epubxp.com/i/313389
66 MMS June 2014 mmsonline.com CNC TECH TALK Columnist Any time I am invited to tour a manufacturing facility, I go on high alert. I look for areas of the shop's operation that could use some help, and I can usually spot a few. Surprisingly, I often find that many different companies seem to be ham- pered by some of the same issues related to wasted productivity. Here are five common productivity killers you should look for the next time you walk through your shop: 1. People squaring vises and other work- holding devices. Although any workholding device used on a machining center must be squared with the machine's table, there are ways to keep a setup person from having to tediously perform this task every time a device is mounted on the table. Look into pinning or keying devices right to the table, or consider using a subplate to which workholding devices can be mounted repeatedly and accurately. In similar fashion, if a qualif ied workholding device is repeatedly removed and replaced, be sure to include pro- gram zero assignment values (fixture offsets) in G10 commands. 2 . Turning center s pindles repeatedl y accelerating and decelerating. When you walk by a turning center, stop and listen for a cycle or two. Do you hear the spindle slowing down as the turret retracts for a tool change? D o e s i t s p e e d u p a g a i n w h e n th e n ex t to o l approaches? Such repeated acceleration and deceleration of the spindle at turret indexes should be taken as a signal that constant surface speed is not being efficiently programmed. The programmer is leaving the machine in constant surface speed mode (G96) during turret indexes. This results in wasted time, because it usually takes longer for the spindle to change speeds than it does to rapid to or from the turret index position. It a l s o r e s u l t s i n w a s te d e l e c t r i c i t y, b e c a u s e e l e c tr i c i t y i s ex p e n d e d eve n d u r i n g s p i n d l e slowdowns, as well as undue wear and tear on the spindle drive system. Have your programmer change the program so that during each tool's retraction to the tool- change position, the machine switches to rpm mode (G97) and the speed needed at the next tool's approach position is programmed. 3. Idle machines. How many CNC machines to do you see sitting idle when you walk through your shop? While some idleness—possibly during setup—may be acceptable, specifically look for times when there's no one around. In many shops I visit, setup people and operators are kept so busy that they cannot keep up with the machines they run. In extreme cases, half the machines regularly sit idle. (In these cases, I often wonder if the company could actually get by with just half the machines it owns.) At the very least, determine the reasons why machines are sitting idle and question the accept- ability of having them do so. Consider focusing more on mac hine u tiliz ation tha n p e r sonne l utilization. 4. People working hard but not neces- sarily working smar t. Here's an example of this that I came across during a lengthy produc- tion run: The cycle ends. The operator opens the door and removes the completed workpiece. He A Waste of Time Here are fve productivity killers to look for the next time you walk through your manufacturing shop. MIKE LYNCH CNC CoNCepts INC. Contact Mike Lynch on MMS Online at mmsonline.com/ experts/lynch.html. 0614_MMS_cnctechtalk.indd 66 5/14/2014 9:51:24 AM