Overcome Drilling Obstacles in Moldmaking
(Written exclusively for MoldMaking Technology magazine)
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When drilling, mold makers encounter many challenges—the most common being hole straightness when drilling deep holes,
poor tool life and excessive time spent in the hole. Not only are correct coolant flow and pressure key to counteract these issues, but also chip evacuation is of utmost importance especially in deep hole drilling. Troubleshooting these challenges begins with knowing the limitations of your tooling and machines, making knowledge about new tooling trends vital to resolving challenges in mold shops.
Time—whether spent in the hole, changing out drills or completing the job—significantly impacts holemaking in moldmaking. Specifically, increasing speeds and feeds influences time spent machining. Oftentimes, machine shops are using outdated tooling simply because it is what they have on hand and are more comfortable with. Whether using twist drills or refurbished IC drills, the extra time you spend resharpening and setting up the tooling often counteracts any added benefit you may have acquired with low-cost tooling. Therefore, it is beneficial to consider adding new cutting tool innovations to your tooling inventory in order to improve cost per hole as well as throughput.
New cutting tool innovations, for example, can outperform the gun drills that are traditionally used in some deep hole drilling applications. The single-effective flute design of gun drills is only capable of half the feed rate seen in recently launched drills like Allied Machine’s T-A Pro.
The double-effective flute design and proprietary coolant configurations in new drills like these offer a higher penetration rate and, therefore, save valuable time on the shop floor.
Effectively changing out drills is a practice that reduces time as well. One of the simplest and most cost effective ways to do this is by having two sets of tools. As one set runs in the machine, the second set is on standby waiting to go in. To allow for quicker turn around time for when tools wear out, an efficient tool room would have pre-setters as well as machinists changing out inserts and tooling away from the machine. If having extra tooling is not practical for you, quick tool changeout can also be accomplished through indexable tooling where insert changes can be made in the machine or at the machine spindle.
Increasing productivity and improving hole quality are additional challenges machinists may face in moldmaking. Coolant flow and pressure are the primary elements that should be adjusted to increase productivity and improve quality followed by choosing the right tool for the job. Chip control, insert geometry, substrates and coatings impact productivity and hole quality as well.
Take deep hole drilling as an example. Deep hole drilling, including air lines, water lines and oil lines, requires knowing how to properly start the hole as well as finish it, which involves using the appropriate drill and coolant for the job. Maintaining balance and stability in deep hole applications relies on chip control and evacuation. The insert geometry being used is a large factor in determining what cutting data you can achieve. If you can create predictably sized chips, they can be evacuated more easily. Improved tooling provides solutions for these challenges and ultimately increases productivity and quality.
Cross holes also present their own set of unique challenges in moldmaking. With cross holes, there are numerous types of interruptions that mold makers deal with. Same-same is where the cross hole and existing hole are the same diameters. Smaller-larger and larger-smaller classify where the hole being created is smaller than the line you are crossing or where the hole being created is larger than the line you are crossing. Finally, half moon holes indicate that a portion of the hole being drilled breaks partway into an existing hole. In all these types of cross holes, there is a lot of interrupted cutting occurring when breaking into an existing hole, which results in tool movement due to opposing forces. Ultimately, this could cause the cutting edge to chip out or potentially fracture the tool. Knowing how much to reduce the feed helps solve these issues, and proper tooling results in fewer failures in machining cross holes due to the nature of the upgraded balanced cutting forces.
Although not as frequently encountered, challenges with boring
and finishing are also present in moldmaking. For the few areas where high tolerance holes are required, digital boring heads are advantageous because they help eliminate operator error when setting boring diameters. Digital boring heads include a readout
that displays the actual movement on diameter when an adjustment is made. This makes compensating for any backlash much easier. Wohlhaupter boring kits, which offer a broad selection of diameter ranges, ultimately satisfy the needs of many mold shops with unique machining application needs because of the versatile setups and improved readiness.
While high finish tolerance is not as necessary in bolt clearance holes or holes that will be threaded, finish is still critical in some mold making applications. For example, water lines need to have a good surface finish because of the fluid dynamic needs. Many mold makers expect the drill they use to give them the finish they need, yet they should be looking at their tooling capabilities more closely in instances where surface finish is critical. Finally, finish is also necessary in some larger diameter holes that will have bushings pressed into them. Here, size and straightness are critical within one or two thousandths of an inch (0.0254mm – 0.0508mm); however, there are drills that consistently machine within this tolerance.
All in all, in order to overcome the challenges of holemaking and finishing in moldmaking, it is necessary to keep up with the newest tooling innovations.