For multi-product, small-batch production of SUS306L stainless steel gate valve stems, we machined the tapered square on a CNC squaring machine, supported by a dedicated clamping sub-sleeve, a taper support in the spindle bore and indexable tooling. According to the customer's machining records, the cycle time of this operation dropped from about 3 minutes to 1 minute 20 seconds per piece, and the staffing arrangement moved from one operator per machine to one operator covering three machines.
Customer Requirements
The customer needed the tapered square machined on stainless steel gate valve stems. The parts cover many varieties, and the batch of each single variety is small, so automatic feeding did not fit the current production plan. With manual loading and unloading kept in place, the customer wanted the per-piece machining time shortened, so that one operator could look after two to three machines.
Previous Machining Method
The original process produced the tapered square on a machining center with a supplementary rotary axis. That took about 3 minutes per piece for this operation, with one operator responsible for one machine. Both ends of the stem and the other turned features were already pre-machined on CNC lathes; this project focuses on the subsequent tapered-square operation only.
Machine and Workholding Solution
Based on the content of this single operation, we produce the tapered square on a CNC squaring machine. The solution focuses on how the workpiece is held, located axially and tooled, while manual loading and unloading is retained, so the production arrangement fits the actual multi-product, small-batch conditions.
Dedicated Sub-Sleeve Clamping
The stem is clamped on the Ø40 mm cylindrical section between the flange and the tapered square, through a sub-sleeve matched to the workpiece. The sleeve has a central through-bore and four slots connected to the bore, one of which is cut through to the outside diameter to leave room for the sleeve to contract during clamping.
Axial Location in the Spindle
The spindle bore carries a taper support used for the axial location of the workpiece. The clamping position and the axial stop work together, so the operator can repeat the machining position at every manual load. The sub-sleeve and the taper support must be matched to the specific part dimensions; they cannot be applied to other specifications by appearance alone.
With both ends of the stem pre-turned, the workpiece is loaded into the sub-sleeve, located against the taper support in the spindle, clamped, and the tapered-square program runs. After the operation the operator removes the workpiece and loads the next one.
Inserts and Tool Holders
Stainless steel machining is prone to built-up edge, so this project uses indexable inserts with matched holders, configured around the clamping conditions. The inserts shown are square type with 8 usable cutting edges; the holder selected for the job is the configuration circled in red in the photo.
After one cutting edge wears, the insert is indexed to the next edge in the normal way. Compared with an insert that offers only 4 usable edges, the 8-edge configuration provides more usable corners and helps control insert consumption. Actual tool life and tooling cost per piece still depend on the insert grade, wear condition and cutting parameters.
Machining Results and Use on Site
According to the customer's machining records, the tapered-square operation on similar stems was shortened from about 3 minutes to 1 minute 20 seconds per piece, a saving of about 1 minute 40 seconds (a reduction of roughly 55.6%). These times cover the tapered-square operation only; they do not include the pre-turning of both ends of the stem, nor the total machining time of the complete valve stem.
Field records from the customer show the staffing arrangement changed from one operator responsible for one machine to one operator responsible for three machines. Under the machining and loading conditions of this project, the operator can stagger loading and unloading across several machines. Whether other projects can adopt the same arrangement needs to be assessed against cycle time, loading time and the workshop layout.
By configuring the machine, the clamping sub-sleeve, the taper support and the tooling around this specific operation, the project shortened the tapered-square cycle time and improved the staffing arrangement across multiple machines. For similar multi-product, small-batch valve stems, we recommend evaluating the solution from the actual part drawing and the existing process chain.
