Many people have never seen a CNC vertical grinding machine with an automatic tool changer (ATC) or know of its many productivity and quality advantages. Vertical grinders can increase profitability, productivity, and part quality by combining multiple operations in one part chucking to:
- Reduce manufacturing cost per square foot (with their reduced floor space requirements)
- Incorporate in-cycle part measuring
- Use pallet changer, automatic tool changer technologies
1. Automatic tool changer
Integration of the ATC into the vertical grinder allows the use of six wheels or more depending on machine size, and more wheels can be qualified and stored on the machine. OD, ID, and facing operations can be done in one chucking. Setup time is reduced by tooling up the machine for the most popular jobs and not having to change or requalify the wheels. This helps with small batch runs by reducing setup time, typically requiring only a fixture and program change. Inserting or removing wheels from the ATC is done through an access door in the side of the machine enclosures, napping one in or out.
2. ID grinding
ID grinding options are limitless on a vertical grinder. Typical horizontal universal grinders offer one or two OD wheels and one ID wheel. If the part to be ground requires significant stock removal, all ID grinding must be done with only one ID wheel. An ATC allows separate wheels for ID roughing and finishing. Part surface finish requirements typically dictate grinding wheel grit size and wheel dressing feed rates, and using a separate wheel for rough grinding allows use of a more coarse-grit wheel for the rough grinding cycle. The majority of grind stock can be removed significantly faster with a coarse-grit wheel with less heat transferred to the part.
Using a separate wheel for finish ID grinding operation allows for finish stock amounts to be reduced to 0.0005" to 0.0010" instead of 0.0080" to 0.0100" or more, increasing life expectancy of the finishing wheel. It provides perfectly sharp abrasives for the removal of the finish grind stock which reduces grinding forces, helping reduce taper by lessening part and/or wheel deflection. The amount of heat transferred to the workpiece falls significantly, with other measurable benefits being better process stability, part quality, and accuracy.
3. Integrated part measuring
Vertical grinding machines offer an advantage with part measuring. Horizontal universal machines typically can’t measure OD and ID surfaces with the probe device; most are used only for end-of-part flagging. Internal and external diameters and faces can all be measured accurately by the same device, and can provide in-machine feedback for size correction. This is useful on larger parts as it is labor intensive to either remove the parts for manual measuring or try to measure them on the machine. The measuring probe has its own high-precision linear axis that allows up and down positioning of the probe for measuring at multiple lengthwise positions. The measuring probe uses a calibration ring before every measurement to correct for thermal expansion that might occur between part cycles.
OD wheel/ID wheel/dressing device interference issues have long been a hindrance for most horizontal universal machines because most are designed for between-center grinding, not chucking work. Many machines require the headstock or tailstock to be moved/removed prior ID grinding. Interference issues between the OD wheel and the table are always a concern, and mounting a dressing device that can reach the OD wheel and ID wheel can be a challenge and must be given serious consideration for every setup. Vertical grinding machines offer unfettered access for every wheel to the workpiece and dressing device without interference issues normally seen with horizontal machines.
5. Pallet changers
Pallet changers are simply not an option for most horizontal machines. Pallet changers allow for medium-to-large parts to be fixtured/loaded outside of the machine, and the machine is running while a new part is being loaded outside of the machine. Large part cycle times often cause machine dedication to one part or operation, but a pallet changer allows multiple parts or operations to run on the same machine and throughput improvements are substantial. Pallet ID recognition allows for the machine to automatically switch programs and tooling between different pallets.
6. Workpiece rigidity
Spindle mounting faces for a typical horizontal universal machine with an 18" part swing are usually around 8". Users are frequently mounting large fixtures with less than 50% face contact. The same-sized vertical grinder offers 100% face contact up to 22". Parts sit against the back of the jaw or fixture, clamping requires less force, and there is less part distortion and better roundness and accuracy. Especially with larger parts, workpiece rigidity is an advantage for vertical grinding.
Most parts are naturally orientated for a vertical machine for automation, so picking of green parts from bins or conveyors by robots or pick-and-place units is simplified, typically not requiring a part flip or reorientation station. The larger and heavier the part, the more this advantage can be realized.
8. Cost of ownership
Horizontal grinding machines have traditionally come with a higher cost of ownership when compared to vertical ones because horizontals have all of their precision axes and spindles in the coolant contamination zone. Grinding swarf accumulation in and around the linear axis and wheel spindles is unavoidable. Verticals have all their linear axes and grinding spindles designed up and away from the contamination zone, helping maintain performance & accuracy longer and with less maintenance. The two big measurables here are maintenance cost savings and increased spindle run time.
9. Reduced cost per square foot
A standard-sized horizontal machine with a 9" workhead spindle center height x 40" distance between centers has a footprint of around 225" x 205". A similarly sized vertical grinding machine with a larger, 22" part swing diameter has a footprint of 106" x 163". Vertical machine design builds the machine upward instead of making it wider, delivering part diameter capacity with half the floor space requirements.
Taiyo Koki Grinding Machines, a DMG MORI Company