Process-reliable back chamfering of 800 bores under challenging conditions with the custom solution "KEMPF RevCut"
Why highly specialized metal parts from Koblenz are used worldwide becomes clear as soon as you gain insight into the manufacturing processes of Deloro Wear Solutions GmbH. Here, no off-the-shelf serial components are produced; rather, complex components are individually developed and manufactured for a wide range of applications. Quality is a key success factor, which is why Deloro aims to switch to complete machining in the CNC machine —even for single parts and small series—ensuring “#burrfree straight out of the machine.” Until now, the right tooling solutions and strategies were missing for some deburring operations. KEMPF, based in Reichenbach-Fils in Swabia and a specialist in such challenges, provided tools like the “KEMPF TriCut” and the custom solution “KEMPF RevCut” for backside chamfering, enabling power plant components to be machined with process reliability from now on.
For more than 50 years, Deloro Wear Solutions GmbH in Koblenz has evolved from a pure foundry into a highly specialized problem solver. Stellite machining remains the core focus and a true unique selling point, which over time has led to the expansion of its capabilities with its own mechanical manufacturing and welding departments. This enables in-house processing of hardened materials, allowing the company to offer customers finished end products as well as repair services. The specialist in heat- and wear-resistant alloys currently employs around 320 people and primarily supplies the food and power plant industries with Stellite-armored parts. These components are used wherever acid, steam, or generally high pressures cause wear issues. Typical components for these applications include double wedge gate valves for pumps, assemblies for screen changers in plastic recycling, as well as control pistons and valve sleeves for hydraulic systems. Since these components are usually used in very large machines, Deloro can machine parts weighing up to four tons and measuring up to 6000 mm in length with diameters starting at 10 mm.
400 Drilled and 400 Back-Chamfered Holes per Component
A small challenge was the production of a steam sieve designed to regulate steam flow in large thermal power plants. The component, made from material 1.4901, a high-temperature resistant stainless steel, with an outer diameter of 180 mm, a length of 300 mm, and a weight of 18 kg, was to be fully machined with process reliability in a batch size of only 24 pieces. The critical aspect was the 400 holes with a diameter of 6.3 mm, each requiring a 120° back chamfer with a diameter of 10 mm.
Since the countersink diameter is significantly larger than the bore diameter, standard tools could not be used. A “solution” was therefore necessary, prompting Deloro to contact the deburring specialist KEMPF from Reichenbach-Fils. Various machining methods were simulated until it was finally determined which strategy would be best for the automated production of the component.
For drilling the bores, the standard drill KEMPF MultiDrill TriCut was selected. This drill, with its 3-cutting-edge geometry, generates up to 50% higher feed rates compared to conventional drills and features a special point design that enables chip breaking, ensuring process-reliable chip evacuation. As a result, drilling operations can be performed significantly faster, more accurately, and with longer tool life.
The MultiDrill TriCut proved to be the first choice for this steel alloy, successfully completing up to 1200 bores, far exceeding Deloro’s expected tool life, tool life, and machining time.
Standard Tools Did Not Deliver the Desired Performance
The second step involved chamfering the bores on the inner diameter of the wall. Initially, the only standard solution considered for manufacturing the countersinks was a right-angle head for internal machining. The right-angle head would have needed to be narrow, long, and robustly designed. However, this was economically unjustifiable due to the investment costs.
Reverse chamfering from the outside using standard tools was not possible because (due to the bore geometry and the given ratio of cutting diameter and angle to the maximum possible shank diameter and length) no process-reliable standard tool is available on the market. The tool geometry resulting from these influencing factors adversely affects tool stability and, due to resulting vibrations, also impacts the workpiece surface and ultimately tool life.
Tests previously conducted by Deloro with spring-loaded folding tools from a specialized company in a neighboring country to circumvent this issue proved suboptimal for this application, even disregarding investment costs, as they did not operate with process reliability and could not achieve acceptable tool life.
The Solution: A Simple Custom Tool
The KEMPF RevCut, a simple yet ingenious custom tool for back chamfering bores, was quickly developed by KEMPF as a custom solution.
The idea behind it: to increase the maximum possible shank diameter determined by the bore geometry by eccentric immersion into the bore. For this purpose, the tool was designed with a cutting edge width that leaves 0.1 mm clearance on each side when plunged aligned with the spindle axis. The shaft was designed with a defined clamping surface in the concentric section, matching the holder’s orientation.
After immersion, the tool is aligned by moving the spindle axis onto the bore axis, the spindle is switched on, and the countersinking operation is carried out “normally.” Initial tests showed that the tool runs very stably, enabling about 800 bores to be back chamfered process-reliably in material 1.4109.
From an economic standpoint, the investment requirement is very low. The carbide cutting edges can be easily replaced and recycled after wear.
Drill "KEMPF ExBurrDrill" Eliminates Additional Chamfering and Deburring
Another task involved machining a component made of material 1.7709, a heat-resistant steel suitable for temperatures up to 540°C. In total, approximately 5,000 bores with a 10 mm diameter, each with a 16 x 90° countersink on the outer diameter, had to be produced.
Due to the requirements, the decision was made to use the KEMPF ExBurrDrill.
The primary feature of this drill is that its cutting edges produce an almost burr-free bore exit. Additionally, the "KEMPF ExBurrDrill" was designed as a step drill with a countersink step for this application.
Unlike the "KEMPF TriCut," the drilling operation alone takes slightly longer, but the entire process is reliably completed in a single machining operation instead of three separate operations: drilling, countersinking, and deburring on the backside. Setup times for two tools and at least two tool changes are also eliminated.
This results in a cycle time reduction of well over 60%, which corresponds to an equivalent increase in machine capacity. The tool life was also convincing, as the tool was only replaced after approximately 40,000 mm, equivalent to about 2,000 bores, to continuously ensure process reliability. Customer feedback was clear: "The drill delivers outstanding results."
Result
Before-and-after image of the steel component:
On the left, the blank, which is pre-turned from a shaft and then reinforced in certain areas with Stellite using the PDA welding process in the welding shop.
After subsequent heat treatment, the component was fully finished on a lathe in two setups, and the backside chamfers at the bores were machined (right).
Working with Custom Tools Creates Additional Capacity
Deloro Wear Solutions GmbH will increasingly rely on process-optimized solutions from deburring specialist KEMPF due to positive experiences, as alternative strategies and tools allow them to save on additional setups, machining time, and labor-intensive manual work while simultaneously optimizing production processes and creating additional capacity.
The quick and straightforward implementation of the custom tooling solution combined with the use of standard tools was the first step in this process.
Image: Kempf field service Marcus Schneider, machine operator Michael Fössing, CNC programmer Andreas Fröhlich, production project manager Andreas Hastrich, process optimizer Tobias Neisins, and machine operator Georg Hedgar (from left to right)