| Re: Best Castings in the Market? |
Subject: Re: Best Castings in the Market? by BeachBum on 2008/12/23 20:37:51 Accuracy is dependant on a lot of variables on each machine..... if its a machine utilizing rotary encoders for the linear axes feedback, then the improvement can be drastic based upon where on the part-program you are at.... in some cases on various contours, the improvement can literally be measured in hundredths, but in just axes 1 or 2 dimensional positioning, measured in just tenths..... But the new technology provides accuracy improvements that easily double, if not triple and yet increase double or triple the capable machining feedrates due to increased processor speeds and high end servo control features I really don't want to bore people with right now..... But, the one thing you can relate to perhaps in the automotive machining and cylinder heads, you'll often here of a porter just needing to "clean-up" the heads.... in many cases this is to remove some hard to reach lips in the cylinder head that even though the tool path was to clean out that portion, didn't finish for a variety of reasons. A cylinder head port is made up of a million different contours, which is the most difficult thing to machine, add in the fact, a cylinder head compounds the problem by being a hard to get into piece of aluminum..... which incidently, is the reason you need 5 axes vs just a tradtional 3 axes VMC. As a note, I didn't touch on what is perhaps the most important aspect for newer CNC advancements in machining cylinder heads, which is block processing speed...... to put in a nutshell, todays CNC's have block processing speeds measured in micro-seconds vs milli-seconds.... what this means, most contoured CNC ports consist of millions of positional points, that the cnc blends together to create a tool path, but each point remains a block of code..... thus the CNC must eat a lot of code to do high speed machining.....A CNC that had a 8ms block processing speed 5 or 10 years ago was considered a high speed CNC.....today, thats literally 10+ times slower than what the modern CNC's can accomplish. What this means is that they can increase the feedrate from 20 ipm to literally 200 or greater provided they have the spindle HP to handle it. This Block Processing Speed issue is a "huge" problem in the industry and if you've ever seen a CNC on a contour start to bump & hesitate, this is typically the reason. The end advantage is that rather than a cylinder head port job spending 6 hours tying up the machine, they can do it the job in just an hour or two taking set-up time into account. This is why they charge between hundredths of dollars extra for the CNC porting, its not the tooling or even manpower, its machine time..... but if that same machine can do 5 or 6 heads in a day vs only 1 or 2...... maybe "our" price will go down  .... we can only hope. |
