28
July
2012

Understanding HSMWorks Adaptive Clearing Toolpaths

Figure-5

HSMWorks Adaptive Clearing toolpaths reduce part roughing time by an average of 40% while reducing tool wear by half and virtually eliminating tool breaking. This article explains how Adaptive Clearing achieves these extraordinary results. After reading this you will understand how this unique technology works and how it can significantly improve CNC productivity and your bottom line.

 

Many shops I’ve visited over the years run milling tools at far less than the optimal cutting feed and axial depth of cut (ADOC) recommended by the tool manufacturer. This lost machining time adds up quickly: Just a 1% reduction in machining time saves about $1000 per year or more on the typical VMC.

Almost invariably the reason given for reduced feeds is tool breaking. The machinists’ tried the manufacturer?s recommended machining parameter but the tool broke. They reduced the axial depth of cut (ADOC) and feedrate (IPM) until the breaking stopped. These “real world” cutting values, which are often well below the manufacturer’s specifications, become the standard applied to future jobs. Thousands of dollars are needlessly wasted.

Most machinists’ realize that the conditions that cause tool breaking exist in only a few critical areas of the tool path: 1) When the tool first engages the material 2) As the tool moves from one cut pass to another, and 3) When the tool moves into an acute angle corner. However, the feed and ADOC used to prevent tool breaking are usually applied to the entire job because manually editing the G-code file is so laborious, tedious and prone to error. I have personally stood at the CNC control and “nursed” a hot one-off job, manually turning down the feedrate override dial in areas where the tool was likely to break and back up for the other 98% of the program to get the job off of the machine faster.

This is not a tool, machine, or CNC programmer problem. It is a software problem. Legacy CAM calculates paths in a way that promotes tool breaking. Figure 1 shows how toolpath is calculated for a legacy CAM system. Notice how the toolpath is based on a fixed stepover distance.

Figure-1

Figure 1: Legacy CAM Fixed Stepover Toolpath

One situation most prone to tool breaking is when the tool moves into an acute angle corner as illustrated in Figure 2 below. Notice that the amount of material engaged by the cutter increases to the full diameter of the cutter as the tool moves into the corner.

 

Figure-2

Figure 2: Legacy CAM = Full Tool Engagement = Broken Tools

The solution in legacy CAM to this problem is to reduce both the chip load (IPR) and depth of cut (ADOC) of the tool. Table 1 compares the manufacturers’ recommended machining parameters versus the actual “real world” values used to reduce tool breaking. This data is for a 3/8 (.375 IN), 3-flute, High Speed Steel, High Helix (60 Deg) End Mill.

table1
Table 1: Manufacturer’s Recommended Parameters vs. Actual Values for 3/8 In End Mill

HSMWorks Adaptive Clearing toolpaths take a completely different approach to calculating roughing toolpaths. Rather than using a maximum stepover distance, Adaptive Clearing lets the machinist specify the Optimal Load of the cutter. HSMWorks creates roughing toolpaths that maintain this constant tool load whenever possible.

Figure-3
Figure 3: Adaptive Clearing Optimal Load Setting

Adaptive Clearing toolpaths look and work radically different than legacy CAM, as shown in Figure 4 below. Notice that the tool never engages more than the optimal load value regardless of its location in the pocket.

Figure-4
Figure 4: Adaptive Clearing Maintains Optimal Tool Load Throughout

Figure 5 shows how Adaptive Clearing enters the acute angle corners. Notice how the tool never engages more than the specified Optimal Load -eliminating the tool breaking condition illustrated in Figure 2.

Figure-5
Figure 5: Adaptive Clearing Eliminates Tool Breaking

Because Adaptive Clearing maintains constant tool engagement the tool can be used for pocket roughing using parameters recommended for heavy peripheral milling. This allows for a higher chip load and depth of cut; resulting in much higher feeds and volume removed. It also means reduced tool wear, since Adaptive Clearing uses the maximum possible depth of cut (ADOC) of the tool: up to 200% or more times the tool diameter (versus just 25-50% of the flutes for legacy CAM).

As illustrated in Figure 6, using more flute length means fewer depths of cut per operation. This combination of deeper cuts and higher feedrates explains why Adaptive Clearing reduces pocket, cavity and core roughing by an average of 40% while cutting tool wear up to half over legacy CAM toolpaths.

Figure-6
Figure 6: Adaptive Clearing Reduces Tool Wear by Using More of the Tool

TEST CASE

The part shown in Figure 7 was used to compare Adaptive Clearing with legacy CAM roughing operations. Part and tool parameters are listed in Tables 2 and 3 respectively. Machining data is from Table 1.

table-2
Table 2: Part Specifications

table-3

Table 3: Tool Specifications

Figure-7

Figure 7: Test Part

RESULTS

Adaptive Clearing toolpaths allow much higher feed rates (156 IPM vs. 65 IPM) and Axial Depth of Cut (.656 IN vs. .375 IN) than legacy CAM. Overall machining time was reduced from 2.63 MIN to 1.67 MIN (37% less).

table-4
Table 4: Results

HSMWorks toolpaths are exceptionally smooth with arc and/or helical on/off moves wherever possible. Because they evenly load the tool throughout the machining operation, the sound produced while machining with HSMWorks is far different than legacy CAM. Legacy CAM produces constantly changing pitch tones -from a growl to a squeal as the tool alternately overloads and chatters. HSMWorks toolpaths exhibit virtually no change in pitch: just a constant sound that says the tool is working at its optimal capacity. The sound is uncanny and truly unique in the CAM world. Experienced machinists will appreciate the significance of this constant sound and what it means in terms of tool life and part surface finish quality.

The previous example used a simple pocket to illustrate how Adaptive Clearing toolpaths because the effect is easier to illustrate and understand in 2D. However, you can expect similar results with far more complex geometry including cavities and cores with thousands of faces, as shown in Figure 8 below.

 

Figure-8
Figure 8: Single pass of Adaptive Clearing Toolpath on 3D Part

HSMWorks encourages potential customers to try the software before they purchase and provides a full working copy (post processing enabled) during this period. This will enable you to see for yourself how Adaptive Clearing toolpaths can help significantly reduce machining time and tooling costs.

  • Tags: Adaptive Clearing, High Speed Machining, HSMXpress

Categories: HSM Tips and Tricks

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