CNC automatic lathes, what you ABSOLUTELY need to know for MAXIMUM use?

Machine tools are one of the most expensive capital investments, and many people may be concerned about purchasing such equipment. This post will explain how to manage “CNC automatic lathe machines” efficiently in operation and how to maximize the benefits of using these machines. If you already have a CNC automatic lathe or are planning to acquire one, this is must-read.

Why METROL came to using the Cincom CNC automatic lathes

We are a user of a total of seven CNC automatic lathes.
(Cincom series CNC automatic lathes from Citizen Machinery, Co., Inc.)

The purpose of the rollout was for in-house production of parts.

Before using the CNC lathes, we had two choices: outsourcing or in-house production using general-purpose machines, but we decided to go in-house production with CNC for the following reasons:

• Long lead times and inability to respond to minor changes.
• Quality control is difficult.
• General-purpose machines cannot produce the numbers and it is difficult to manage costs
• Know-how on in-house machining and NC does not accumulate within our company.

Reasons WE chose Citizen’s Cincom for our CNC automatic lathe

Among many choices, why METROL selected Citizen Machinery’s Cincom series:

• Fast service in case of trouble and good reputation among our partners who were already Cincom users.
• It is easy for even beginners to use, and we have found it fits our motto, “small number of people, multi-unit tasks”.
• Cincom has an LFV (vibration cutting) function to help avoid chip issues.

Having a variety of equipment brands increases the number of operations to learn.　Our policy was to use standard models from the same manufacturer, and we ultimately selected Citizen Machinery’s Cincom.

Two key issues to be aware of before investing in a CNC automatic lathe

Although not limited to CNC automatic lathes, two key issues must be considered when investing in automated machines in general:

The first one is the risk of “continuous defective part production in continuous machining”.

For example, suppose that when 1,000 parts are continuously machined, and machining defects began to appear from the 500th part.
In the worst-case scenario, the remaining 500 parts will all be defective, wasting material cost and machining time. In reality, we need to inspect all 1,000 parts because it is impossible to determine when the defects started, and this requires a lot of inspection man-hours.

Tool chipping and thermal displacement are the most common causes of processing defects, but once a defect is found, it is unlikely that the product will return to good quality. It is an ironclad rule to stop the machine as soon as possible after a defect is detected.

The second is “dimensional measurement of the workpiece after shaving”

The more you make, the more inspection man-hours you will need.
If defective products are found, we must sort out the good products from the defective ones and identify the cause.

Inspection rules vary from user to user, but here is the summary of the challenges of processing large quantities at a time:

• Even if there are no defective products, inspection man-hours are required for every product made.
• Difficulty of knowing how many defects have occurred since the first defect. (Once defect is detected)
• There is a risk of continuing to produce defective products.
• Early improvement of defective processing becomes difficult.

If you have the manpower and budget to do so, a “full inspection” is a good idea, but it is important to set rules for efficient inspections.

What is an operation that efficiently maximizes CNC automatic lathes?

We avoid the above mentioned two challenges by performing “on-machine measurement”.

After machining a certain number of pieces, we check the workpiece dimensions (inside and outside diameters) while clamping using a touch probe. In the event that the touch probe detects an out-of-tolerance defective product it will perform the following 3 steps:

1. Stops the machine with an alarm
2. Equipment Maintenance
3. Retry the processing

Let us explain the operation and benefits of this “on-machine  measurement” using examples.

[Case Studies] ADVANTAGES of “On-machine measurement” on a CNC automatic lathe

For example, suppose that in a 1000-workpiece machining cycle, the workpiece is measured with a touch probe once every 250 pieces.
If the on-machine  measurement detects a defective product, the machine stops with an alarm to prevent further processing. (See figure).

When the machine in Process 6 has stopped, the defect cause is immediately identified, and maintenance is performed on the equipment to prevent defects in Process 7.

Advantages of “on-machine measurement” that YOU should know

The following three advantages can be achieved by stopping the machine when a defect is detected:

1. Workpieces from lots that are determined in Process 1 and 3 to be GOOD by on-machine measurement do not require inspection.
2. Only workpieces from lots with errors (Process 5) need to be sorted as defective.
3. Future machining defects (process 7) can be prevented.

In other words, on-machine measurement will help prevent the following three losses:

1. Reduced man-hours required for 750 inspections (Processes 1, 3, and 7)
2. Material cost for 250 pieces (Process 7)
3. Processing time for 250 pieces (Process 7)

The person in charge of the equipment must identify the cause of a processing defect as soon as it occurs. If it took long time, the situation may change, and it may be difficult to locate the cause of the problem.
If the cause is identified immediately, it will help prevent recurrence and make it easier to take countermeasures.

 Advantages of “on-machine measurement” from the viewpoint of MAN-HOURS

On-machine measurement also reduces man-hours associated with workpiece measurement, such as moving people and removing workpieces.

In the past, workers had to remove the workpiece from the equipment, carry it to the measurement location, and perform, which required man-hours. On-machine measurement with a sensor while the workpiece is clamped after machining eliminates “removal” and “transport time to measurement”.

What types of touch probes can be used on CNC automatic lathes?

Although touch probe “on-machine measurement” has many advantages, some may be hesitant to install it for the following reasons:

• The probe itself is too large and interferes with the tool or spindle.
• The mounting bracket would take up extra tool holders.
• Worried about the accuracy of on-machine measurements.
• Measurement time increases takt time.

Against this backdrop, METROL has developed the K3S series of ultra-compact touch probes with a body diameter of φ19.05 mm for equipment with limited space for installation, and have them on our  own equipment.

The diameter of the probe body is thinner than prior versions so that the probe body fits completely into the tool holder.

Unlike conventional touch probes, the main body is not exposed, so it does not interfere with the spindle or workpiece and does not take up extra space in other tool holders.

What is the actual reason for “wanting to PRIORITIZE tact time over on-machine measurement”?

There is a real concern that on-machine measurements will lengthen “tact time”.
In particular, many prioritize processing (takt time) and sort out defective products later and replace them with good products. In this case, the processing time spent on defective products, sorting and additional man-hours are not taken into account in the takt time, and this is often OVERLOOKED.
If the process load associated with machining defects is greater than the measurement time, there is much room to benefit from on-machine measurement.

[Movie]”On-machine measurement” by CNC automatic lathe

We use touch probes to measure the inner and outer diameters of workpieces.

You can see how we measure the diameters of workpieces in this video. Because of the very small size of the parts, it is clear that measurement with a probe is more efficient than manual measurement.

What is the concept of “on-machine measurement” on an automatic lathe, and how precise is the measurement?

The greatest advantage of “on-machine measurement” with touch probes is that “measurement can be performed automatically in the flow of machining conditions where the workpiece is accurately positioned.

Meaning, the Touch Probe allows the machine tool to act as a simplified 3D measuring machine.

In contrast, when measuring manually outside the machine, the positioning conditions change because the workpiece is removed after machining. In addition, the level of measurement skill varies from operator to operator, and there is a risk of human error and measurement error with tools (calipers and pin gauges).

How to equip a touch probe on a CNC automatic lathe?

To install touch probes on new equipment

A program is required to install a new touch probe.
Please contact us or the manufacturer first.

For Citizen Machinery, it can be mounted on the A20, L20, and L12 of the Cincom series.

To retrofit an existing automatic lathe

You may need to check with the manufacturer whether the hardware and electrical specifications of the equipment are in line with your requirements.
Please contact us or the manufacturer at your convenience.

In conclusion:

While the introduction of automatic lathes makes it possible to machine a large number of items at once, a single wrong element and a large number of defective parts could be made.

In these days of human resource shortages, why not try efficient operation while taking advantage of these sensor technology?

We also offer rental samples of touch probes for evaluation purposes.

Contact and Product Information

Our engineers will respond to any questions regarding product usage methods or requests to customize products.
We can provide our best support if details about application, usage environment and what kind of workpieces will be detected can be provided.

Use our contact form below to contact us.